Chapter 6: Collapse of the Closed Room
Yozuki was drinking tea in the dining hall, waiting for a call from Kuzushiro. Kuzushiro had declared that the mystery had been solved, gathered everyone in the dining hall (even though they were already there), and disappeared somewhere. It seemed like he was preparing something. Yozuki, who had gotten bored, joined Mitsumura, who was still eating at a nearby table. She suddenly asked her something, just wanting to make small talk.
“Do you think Kasumi's actually managed to solve the locked room?”
Mitsumura shrugged and said “Well, what do you think?”
Kuzushiro returned to the dining hall at that moment. It felt like he'd kept them waiting for a while, but in actuality, he'd only been gone for less than 30 minutes.
“Okay everyone, please come with me.”
Kuzushiro said that as he led Yozuki and the others out of the dining hall. It was an extremely formal affair. Yozuki thought it didn't suit him. Well, any intelligent behavior didn't suit Kuzushiro.
He guided them to the third floor library in the west building. The room where Yashiro's corpse had been discovered. Of the five locked room murders that had taken place in this mansion, this was the only one that remained unsolved.
Kuzushiro looked at everyone. “Everyone” being the five people currently in the mansion, minus Riria. Specifically, Fenrir, Ishikawa, Meirozaka, Mitsumura, and Yozuki. Including Kuzushiro himself, one of the six people gathered there was the culprit who'd killed Yashiro. And the one who'd made the locked room...
“Well then, everyone.”
Kuzushiro began his announcement.
“I will now begin solving this locked room mystery.”
“Well,” Kuzushiro declared arrogantly, looking around at the group of five. And he began talking like this:
“Before I begin my deductions, there is something I would like to confirm. Are you all aware of the Locked Room Classification List created by the Ministry of Justice?”
Everyone looked at each other, confused.
“Yes,” Mitsumura said first, “of course I do.”
“It's common knowledge,” said Fenrir.
It was? Yozuki didn't know it. But Ishikawa said “No, I don't know that,” and Meirozaka followed with “Me neither.” That made her feel a little better. Yozuki proudly raised her hand and announced “Yes, I don't know anything!” Mitsumura and Fenrir looked at them like they were aliens. ...Didn't those people just spend way too much time in locked rooms?
“So, what's the Locked Room Classification List?” When Yozuki asked outright, Kuzushiro shrugged his shoulders.
“As the name suggests, it's a classification created by the Ministry of Justice after Japan's first locked room murder three years ago. It classifies tricks, and according to the list, there are only fifteen different types of locked room tricks in existence.”
Fifteen types? Yozuki thought there were far fewer.
“In other words, no matter what locked room murder there is, its trick will always fall into one of these fifteen categories. Now, allow me to actually write out the Locked Room Classification List. Here is the classification of locked room tricks created by the Ministry of Justice.”
Somehow, a whiteboard had materialized in the library. Kuzushiro wrote down the list created by the Ministry of Justice with a black marker.
Closed Room Classification List (classification of all tricks, etc. to create a locked room)
① Return the key used to lock the door to the room through a gap, I.E. under the door.
② Turn the thumb turn or reset a similar internal lock via some means.
③ Escape via secret passage.
④ Removing the hinges and reapplying the door from the outside.
⑤ The victim was the one to lock the door.
⑥ The culprit hid inside the room.
⑦ A non-locked room was mistakenly identified as a locked room.
⑧ The actual location of the locked room differs from the location where the body was discovered.
⑨ Duplicate keys.
⑩ The key is secretly returned to the room in the chaos following the discovery of the body.
⑪ The key left in the room is a fake, replaced with the real key later.
⑫ Secret, rapid murder.
⑬ The victim was dead before the room was locked.
⑭ The victim was killed in the locked room from outside the room.
⑮ The victim was killed in the locked room from inside the room.
After writing out all the categories, Kuzushiro capped the marker. He then tapped the whiteboard with the cap.
“Since there are only these fifteen types of locked room tricks, the trick used in this case must definitely belong to one of them. In other words, if we examine them all one by one, we will eventually arrive at the truth.”
“What, you mean we're going to be testing all fifteen possibilities?” asked Yozuki.
“That's how it is. So, even though it might take a while, I'd like you all to listen to it. It's kind of a tradition in locked room mysteries.”
A tradition... She didn't understand what he was saying.
Still, Yozuki nodded slightly. Everyone else nodded as well. So, they heard him out. He gave a long, rambling speech – also a tradition of locked room mysteries.
“Then, let's begin by considering ①.”
With the group's consent, Kuzushiro began speaking in a formal manner. Hearing him, Yozuki turned her attention to classification ① written on the whiteboard. It said “Return the key used to lock the door to the room through a gap, I.E. under the door.”
“You could call this the most basic locked room trick,” Kuzushiro said. “I don't need to explain at this stage, but it's a trick where the key is used to lock the door from outside the room, and then returned to the inside of the room using thread or some such through a gap under the door. But in this case, that trick is impossible. Why do you think that is, Mitsumura?”
Mitsumura, who'd suddenly been nominated, felt annoyed.
“...Why are you asking me?”
Kuzushiro shrugged.
“It's easier to make deductions of you have an assistant.”
“No, I understand that. I'm asking why I've been appointed as assistant. I feel like I'm being looked down upon and it makes me very uncomfortable.”
Mitsumura suddenly turned away. Funny, that was how Kuzushiro had felt when she used him as an assistant in her deduction before. He told her so, and a fruitless discussion flowed from there. They bickered for about five minutes.
Mitsumura finally relented and, reluctantly, accepted the role of assistant.
“Fine. I didn't want to have to explain something this basic, but I'll answer you.” She took a deep breath. “It's extremely easy to deny ①. First of all, there are no gaps in the room, under the door or anywhere else. That's why the key couldn't have been restored to the room. The key was found inside a jam jar with its lid firmly closed, and there is no evidence of any trick having been used inside that room. Locked room tricks aren't magic – they can't violate the laws of physics. Since neither 'a way to get the key into the room' nor 'a way to close the lid without leaving a trace' exist, we can say with certainty that ① could not have been used.”
Kuzushiro nodded and said “Yes, I agree.” Mitsumura pouted and replied “'Yes, I agree', you're so arrogant.”
At any rate, option ① had been denied. Kuzushiro struck out ① from the whiteboard with a single vertical line. Then he indicated option ②.
“Then next is the second category, which involves turning the thumb turn on the inside of the door in some way. But this is also not possible. Mitsumura?”
“Alright, I guess I'll answer this one, too,” she said grumpily. “It's for the same reason as ①. The thumb turn on the inside of the door was covered by a gachapon lid, making it unusable. In other words, if the culprit did use a trick, they must have also prepared some kind of mechanism to attach the lid to the thumb turn after the mechanism that locked the door did its work. But no trace of these mechanisms were found anywhere. There's no gap under the door, so the devices couldn't have been retrieved, either. As I said, locked room tricks aren't magic.”
Kuzushiro nodded and struck out ② with his marker. Thirteen classifications remained.
“Next comes option ③, 'escape through a secret passage'. Isn't this one simple? There is no secret passage in the entire west building, where the crime scene was located. So we can ignore this one.” Kuzushiro struck out ③. Then he indicated classification ④. “Next, ④, 'removing the hinges and reapplying the removed door'. You set the inner lock of the removed door to extend the deadbolt, then reinstall it from outside the room. Mitsumura and I investigated this possibility earlier, and we concluded that it was impossible. The screw holes of the hinges aren't accessible while the door is closed, so we can eliminate this one as well.”
Option ④ was stricken out.
“So, ⑤. The possibility that 'the victim was the one to lock the door'. This can mean it was a suicide and not a murder, or that the victim was stabbed outside the room, ran inside, locked the door to keep the culprit away, and died of their stab wound. How can we eliminate this one?”
“Right, right, it's my turn again.” Mitsumura was still acting moody. “This, too, is frightfully easy to deny. The victim, Mr. Yashiro, had wounds inflicted after death – that was revealed by the absence of vital reactions at the autopsy. Even if the one who locked the door initially was the victim himself, the culprit was still there, attacking him after his death. In that case, how did his attacker escape the locked room? It must have been using one of the remaining fourteen classifications.”
Didn't that mean they were back to square one? The fifth classification got them nowhere.
Kuzushiro struck out classification ⑤.
“Next, ⑥, 'the culprit was hiding inside the room'. There was nowhere in that room for the culprit to hide. Rejected!”
Classification ⑥: struck out.
“Next is ⑦, 'a non-locked room was mistakenly identified as a locked room'. This can mean that there was, for example, something barricading the inside of the inward opening door, preventing it from opening. Because the door wouldn't open, we mistakenly thought it was locked. But this door really was locked, so we can remove this option.”
Classification ⑦ was removed.
“So then, ⑧, 'The actual location of the locked room differs from the location where the body was discovered.' This one's a bit complicated, but to give an example, say the characters hear a scream coming from Room A and break the window to see what's going on inside. But before they actually enter the room, they leave for whatever reason, and when they return to the scene, they are misled by the murderer's trick and arrive at Room B instead of Room A. The body is found in Room B. The window of Room B was broken just like the window of Room A, but the window of Room B was broken in advance by the murderer. Since the window of Room B was broken, it wasn't actually a locked room. But this trick isn't usable in this case. Why not? Mitsumura.”
“Yes, Mr. Kuzushiro,” Mitsumura moaned like a lazy student who'd been called upon in class. “We broke the window and went inside immediately.”
“Yes, but there's also another reason, isn't there?”
“You mean because the scene was on the third floor?”
“That's it.”
Struggling to follow the conversation, Yozuki raised her hand.
“Mr. Kuzushiro, what does the scene being on the third floor mean?”
“Teaching assistant Mitsumura will explain.”
“I'm your T.A. now?” Mitsumura rolled her eyes. Then she sighed and said “It's simple, Yozuki. In this case, the scene was on the third floor, and the only room on the third floor is the library. In other words, there's no way we could have mistaken it for any other room. This trick requires the existence of another room with the same floor plan as the crime scene, on the same floor as the crime scene. Well, there is a similar trick where a room with the same floor plan on a different floor is swapped for the crime scene, but we all know that the west building is three stories tall, and that there are no rooms on the first or second floor have the same floor plan as the library, so that trick isn't usable either.”
I see, Yozuki thought. Option ⑧ was stricken from the whiteboard.
“Next, ⑨, 'Duplicate keys'. There are no duplicate keys. Deleted.”
Pattern ⑨ was easily erased.
“Next comes ⑩, 'returning the key to the room while the body is being discovered'. This is the trick where the culprit secretly places the key used to lock the door on the floor while everyone is focused on the body. If it's done correctly, it creates the illusion that the key was there from the beginning. But in this case, the key was left in a sealed bottle right next to the body. Mitsumura found it right away, and I watched her do it, so this trick can't be used.”
So he also struck out ⑩. The number of classifications left was gradually decreasing. There were only five left.
“Next is ⑪, the category of 'the key left in the room was a fake, to be replaced with the real key later'. The master key left in the room was definitely real, and there were no opportunities to replace it. The jam jar the key was in has been in Mitsumura's possession this whole time. And she couldn't have replaced it herself. I was secretly keeping an eye on her the whole time.”
“Really? That's disgusting.”
“Anyway, option ⑪ can be eliminated.”
And away it went.
“Next, ⑫, 'secret, rapid murder'.”
“I've heard this one's also called sleight-of-hand murder sometimes,” Meirozaka said.
“It's one of the most classic of the classic of locked room tricks,” Kuzushiro said. “When the locked room was broken into, the victim was still alive, just drugged unconscious. The first person to approach him asks 'Are you okay?' However, that person is actually the culprit. While pretending to check if the victim was okay, the culprit stabs them to death with a hidden blade. In other words, they quickly committed the murder in front of everyone.”
Yozuki understood the concept, but it was still quite a shock to think that someone would deliberately commit murder in front of witnesses.
“But this trick does have one drawback,” said Kuzushiro. “The time of discovery and the time of death will be extremely close. Therefore, the autopsy can determine whether or not it's possible for the rapid murder trick to have been used. Dr. Ishikawa.”
When Ishikawa's name was suddenly called, the man himself trembled in surprise. “Please don't call me like that all of a sudden,” he said, still smiling.
“So, what can I do for you?”
“The estimated time of Mr. Yashiro's death. How long had he been dead when we found the body?”
“I'm pretty sure...” Ishikawa searched his memory. “It had been about two hours since he'd died.”
“Then there's no possibility that a rapid murder was committed.”
A vertical line went through ⑫. Three left.
“Next is ⑬. 'The victim was already dead before the room was locked.' For example, the key to the room was available in the morning, but in the afternoon, it was in view of people and could be proved to have not been used. Because the victim was killed in the afternoon, the key wasn't usable and the room couldn't have been locked. However, the victim was actually murdered in the morning, while the key was available, meaning the door could have been locked to the culprit's heart's content. Although, the key was under surveillance, so this isn't really a locked room, per se... But, this trick...” Kuzushiro looked at everyone. “Is completely irrelevant. Because in this case, the master key was found inside the room. Classification ⑬ is absolutely impossible in any case where the key was found inside the room. That's why we can remove this one.”
Option ⑬ was removed. Finally, only two possibilities remained.
“Next up we have classification ⑭.” Kuzushiro tapped the whiteboard with the marker's cap. “The possibility that the victim was killed inside the room from outside the room. For example, using a powerful electromagnet to knock over a metal bookshelf inside the room and crush the victim. But why wasn't this possible?”
“Oh, me! Me, me, me!” Yozuki raised her hand. With a smug smile, she said “Because in this case, the victim was not crushed under a bookshelf.”
“............”
“What?” Yozuki looked at Kuzushiro. Kuzushiro met her with eyes full of pity. She didn't understand.
“Well, no. teaching assistant Mitsumura, if you would.”
“Yes, sir,” Mitsumura said with a shrug. “It's simple. The victim, Mr. Yashiro, was not killed in the library, but in his own room.”
She still didn't understand. Sure, Yashiro was killed in his own room, and his body was moved to the library afterwards. So what?
“You still don't get it?” teaching assistant Mitsumura asked.
“I don't get it,” Yozuki said.
“Then I'll give you a hint. It's quite simple,” Mitsumura said with a slight giggle. “The culprit carried the body to the room. Afterwards, they performed a class ⑭ trick. Don't you find that odd?”
“Odd? Oh, I see...”
Yozuki finally noticed.
By the time the body was brought into the room, the victim was already dead. After all, he was a corpse. However, in that case, classification ⑭ – 'being killed inside the locked room by a culprit outside the locked room' – was no longer possible. That was because classification ⑭ assumed that the victim was the one to lock the door.
“Incidentally, if the victim had still been alive when they were brought to the scene of the crime, we'd run into the same issue as in ⑤, so it would still be denied,” Mitsumura added.
Seeing that Yozuki was satisfied, Kuzushiro erased option ⑭. And then there was one.
“Finally, classification ⑮,” Kuzushiro declared. “Killing the victim inside the locked room from inside the locked room. This is the classification of traps set up inside the room, like knife launching devices set on a timer. The victim locks the door themself, sits on the couch, then gets stabbed by a flying knife. That's the trick. And it doesn't work. It's the same problem as with ⑭. The victim's corpse was moved from another room, so ⑮ can be eliminated for the same reason as ⑭.”
Classification ⑮ was stricken from the list.
“Eh...?”
Yozuki let out a noise. Everyone else looked at the whiteboard, looking perturbed. There were fifteen types of locked room tricks written out there. And Kuzushiro's reasoning had eliminated all of them.
“What are you saying, Kasumi?” Yozuki asked, confused. “It doesn't fit any of the fifteen types of locked room tricks.”
Kuzushiro shrugged a bit.
“That's how it is. No matter what trick we use, we can't recreate this specific locked room.”
“That's it...?”
Confusion turned to despair. So how had the scene become a locked room? Locked room tricks weren't magic; Mitsumura, who had listened to Kuzushiro's deduction earlier, had said so. If it wasn't magic, they couldn't do anything physically impossible.
But...
No matter how she looked at it...
“Magic-”
“It's not magic.”
Kuzushiro cut Yozuki off.
“Indeed, no matter how you look at it, it seems this is an impossible crime that can't be replicated. But... it can. There is one trick that can explain this impossible situation. It's an extremely simple trick that doesn't fit into any existing category.”
“That's...” Yozuki said. It didn't belong to any of the fifteen classifications of locked rooms... That made it a sixteenth trick outside the Ministry of Justice's classifications.
“Just what is it?”
When Yozuki raised her voice, Kuzushiro allowed himself a small smile.
“I'm going to recreate it now. Well, Mitsumura.”
“What?”
“Please play the role of the corpse.”
Mitsumura rolled her eyes and sulked without shame. “Why me?” she asked, pouting.
“Please, teaching assistant Mitsumura.”
“I'm not your teaching assistant.”
“Fine, then light speed detective clown.”
“Why would a light speed detective clown play the role of a corpse?”
The two of them argued for a while. Again. Eventually, and with great reluctance, Mitsumura relented and accepted the role of the corpse.
“Now, let's recreate the trick,” Kuzushiro announced, and then he pretended to stab Mitsumura with a knife. “Guh!” Mitsumura fell to the floor. “First, the culprit killed Mr. Yashiro and dragged him to this room. Well, they probably carried him on their back, actually...” Kuzushiro said.
“And then,” Kuzushiro took a key out his pocket. It was the master key to the west building. “They put this in the jam jar and closed the lid.”
Kuzushiro picked up the jam jar from the corner of the room. He put the master key inside and closed the lid, as advertised. He placed it next to Mitsumura, playing the role of the corpse. The master key had been rendered unusable.
Kuzushiro looked around at the group.
“And now, I will create the locked room.”
Everyone except Mitsumura, who was still playing dead, was confused by his words. Fenrir, Ishikawa, Meirozaka, and of course Yozuki. They all wondered how he was planning to create a locked room like this.
As everyone looked at him in puzzlement, Kuzushiro leisurely opened the door and stepped out into the hall. The door slammed shut. Kuzushiro's voice from outside the room passed through the closed door.
“I'm going to lock the room now.”
As he said that, they heard the sound of something being inserted into the keyhole. Immediately, the thumb turn began to rotate.
With a click, the door was locked.
“Eh...”
Yozuki's voice died. She immediately ran to the door. She grabbed the doorknob and pulled. The door didn't open. It was really locked.
What? How? Why was the door...?
Still confused, Yozuki unlocked the door. She immediately began expressing her confusion to Kuzushiro when he opened the door and stepped back into the room.
“How on Earth did you do that?” she asked, thoughts a jumbled mess. “How were you able to lock the door?”
“Ah, with this.” Kuzushiro took “it” out of his pocket. “I used this to lock the door.”
What Kuzushiro held in his hand was a key. The a long, sleek key like the ones to the rooms in the west building. The confusion was only getting worse. He'd used that key to lock the door. Did that make it a...
“Duplicate key?”
Kuzushiro smiled at Yozuki's words.
“There are no duplicate keys. The only thing that can lock the library door is the master key in the jam jar. That's the basic premise of this case, right?”
“B-But... If there isn't a duplicate key, then what's that?”
“Oh, this?” Kuzushiro held up the key in his hand. “This is the key to my room.”
Yozuki burst out laughing. She thought Kuzushiro was joking.
“What are you talking about, Kasumi?” she asked, as if trying to admonish him. “There's no way you can use the key to your room to lock the library door. The only thing your room key can lock is your room, right?”
That was something even a child could understand.
But hearing Yozuki's words, Kuzushiro shrugged. He looked like he was the one admonishing a child.
“Yeah, so...”
He explained.
“I replaced the doors. I removed the hinges – from the door to my room and the door to the library, where the crime took place. Then I swapped the door to the crime scene with the door to my room. Would that let me lock it with my key?”
“You... swapped the doors?”
I nodded at Yozuki. All the rooms in the west building, including the library, had identical doors. So by removing the hinges, you could swap them with the door of any other room. The culprit took advantage of that to replace the door to the library with the door to their room. Then, since the door on the library was actually the door to their room, the library could have been locked with the key to their room. That allowed them to lock the door while leaving the master key behind.
I looked at Mitsumura, who was still lying on the floor playing the corpse. Her eyes had gone wide in surprise, and she softly murmured to herself “So you actually saw it.” I was probably the only one to hear her. I nodded.
Then I looked at Yozuki. She tilted her head. “What?” She didn't seem to have realized, but it was actually thanks to her that I'd been able to find this locked room trick. This morning, when I'd mixed up the lids of the marmalade and apple jam jars, Yozuki had opened them back up and swapped the lids. The moment I saw that, I'd realized the door swapping trick. At the same time, I'd remembered when I examined the hinges of the library door with Mitsumura. At the time, I'd thought that one of the screws on the hinge was loose, and Mitsumura had told me it was just my imagination, but she was wrong. There was still a trace of the locked room trick left at the scene.
Removing hinges and removing and installing doors is something contractors and other repairmen do all the time, and even an amateur can pull it off quickly if they have practice. And, as I'd confirmed on the first day, all the doors in the west building had flush doors with hollow interiors. Since it was made of wood, the door probably weighed about 10 kilograms, easily replaced by anyone here.
And this trick also explained two things that I had been wondering about for a while now.
“There are two puzzling aspects of this incident,” I said, holding up two fingers on my right hand. “One is: why did the culprit move the body to the library? The other is: why did the culprit remove the piece of tape left on the door?”
At a glance, they both appeared to be meaningless actions. But of course, they were done with good reason.
“Let's start with the first question. Why did the culprit move Mr. Yashiro's body from his room to the library? There's no obvious differences between the two rooms that would impact the case. But that wasn't the case for the culprit. They needed the body to be found in the library.”
Everyone, especially Yozuki, looked at me like I was speaking Swahili. “What do you mean?” she asked, and I responded “It's simple.”
“Because this library doesn't have its own key. It can only be opened with the master key. That's important, because this door swap trick has a major downside. Let's say the culprit did try to use this trick to lock the door to Mr. Yashiro's room. In that case, they'd need to leave behind both of the keys that could be used to lock the room – the master key, and Mr. Yashiro's room key. If they didn't leave every key that could lock the door in the room, it wouldn't be a locked room to begin with. So, the culprit leaves both keys in the room, then locks the door with their own key. And the locked room is complete. But it isn't perfect. It might look like it is, but it actually isn't.”
“What are you saying?” Yozuki asked with a tilt of her head. “I don't see anything wrong with that.”
“The problem is the replaced door,” I said. “The culprit put their own door on Mr. Yashiro's room. That would allow them to lock the door with the key to their own room. But inside, there would be the key to Mr. Yashiro's room. And even though it was Mr. Yashiro's room, that key would no longer be able to lock the door. That's clearly abnormal, and moreover, the culprit had created a locked room and left that key behind. The first thing any detective does upon realizing they've been confronted with a locked room murder is check if the key is real. When the key didn't lock the door, the detective would have concluded that the key was a fake, and the locked room would fall apart.”
In actuality, the key to Yashiro's room left inside would have been real. But the detective, not knowing that the door had been replaced, would have assumed that the key was replaced with a similar looking one that didn't work. Even though it was actually a real key, it would have been written off as a fake.
“But the library doesn't have its own key,” I said. “It can only be locked with the master key. And that master key can lock every door in the west building. Including the door to the culprit's room.”
In fact, when Yashiro's body was discovered, Mitsumura and I had checked if the master key left in the room was real. We made sure that the key left in the room actually locked and unlocked the door. But at the time, the door to the library had been replaced with the door to the culprit's room. But the master key could lock the door to the library and the culprit's room. So even though the door had been replaced, the master key wouldn't expose the replacement. That's why the culprit brought Yashiro's body to the library. It didn't have its own key, so it could only be locked with the master key.
“That is the answer to the first question, 'why did they move the body?'.” I said. “The second question, 'why did they remove the piece of tape?', also has a simple answer.”
The piece of tape that didn't have any reason to be removed. The reason why the culprit went to the trouble of removing it was...
“They didn't. After Mr. Yashiro's body was discovered, the culprit waited for us all to go back to sleep and swapped the doors back to their original state. When they did, the piece of cellophane tape attached to the door at the crime scene was moved to the culprit's room. That made it look like the culprit had removed the piece of tape.”
And that piece of tape was probably still stuck to the door of their room. So if we went and checked all the doors now, we could find them out right away. But that wouldn't be necessary. Because I already knew who the culprit was.
And I wasn't the one who'd found them.
“Mitsumura.”
That's why I said her name. She, who had been lying on the floor playing the role of the corpse, stood up and gave me a distrustful look.
“What?”
“Please tell everyone who the culprit is.”
That made her even more suspicious. She scowled and pouted as she spoke.
“Explain it yourself.”
“But you were the one who realized their identity, right?” I shrugged. “I'm not shameless enough to take credit for a borrowed deduction.”
Mitsumura laughed a bit. “'I'm not shameless enough', you're so arrogant,” she murmured, then stroked her long black hair.
“Alright, we'll switch roles as detective. There are now six suspects, including myself and Kuzushiro. We will use logic to determine which of them is the culprit.”
“The key is the playing card left at the scene,” Mitsumura began. “The nine of hearts was found in the pocket of Mr. Yashiro's corpse. And that playing card was stolen from Miss Riria, the culprit of the previous four murders. She kept it in a secret compartment in her smartphone case.”
“A hidden compartment?” Fenrir tilted her head. “There was something like that?” Mitsumura explained it to everyone. The protruding decoration on the smartphone case – the crown – and how if you pulled it five times then pushed it five times, the secret compartment would be revealed.
“The night Mr. Yashiro was killed, Miss Riria's smartphone had been left on a couch out in the lobby,” Mitsumura said, “So theoretically, anyone could have had an opportunity to steal a card from it. But having an opportunity doesn't mean it was possible, does it? If they didn't do this exact ten step process, the secret compartment wouldn't have opened. Then they couldn't have stolen the cards. And Miss Riria told us that she never told anyone else about this secret compartment.”
In other words, no one other than Riria could have taken the card out of the smartphone case. They wouldn't have even known they were in there.
“But the culprit did steal the playing card from Miss Riria,” Dr. Ishikawa said with a thoughtful look on his face. “So the criminal must have known how to open it somehow. If you think about it, they must have secretly watched her take the cards out of the smartphone case.”
“But that would be difficult,” Mitsumura shook her head. “Miss Riria said she only ever opened her phone case in her room, so the culprit wouldn't have been able to easily spy on her.”
“Oh, what if they set up a hidden camera?” Yozuki had apparently just thought of the idea. “If they set up a camera in Riria's room, they would be able to see what was going on inside.”
Mitsumura shook her head.
“Unfortunately, that isn't possible either.”
“Eh, why not?” asked Yozuki.
“Because Miss Riria owned a hidden camera detector. She used that equipment to search the entire building for hidden cameras. Miss Riria is our nation's most notorious assassin. If there were any hidden cameras, I'm sure she would have found them.”
“But maybe the culprit snuck into her room after she searched for the hidden cameras,” Yozuki said. But Mitsumura shook her head.
“No, that isn't possible. The doorknob of Miss Riria's room had an auxiliary lock of the sort sold in hardware stores. As a result, I had to get the key to that lock to investigate the room. Even if I'd used the master key to the west building, I couldn't have entered the room. Miss Riria must have applied that lock after entering the room. It would be impossible to sneak in and plant the hidden camera afterwards.”
Yozuki nodded at Mitsumura's explanation and said “I see.” In her place, someone else started making noise. “Then what about something like this?” said Miss Meirozaka.
“Miss Riria didn't start her search for hidden cameras until after she took the cards out of her smartphone case. Later, she used the hidden camera detector to find the camera, but by then it was too late and the footage had already been transmitted to the culprit.”
Mitsumura shook her head again.
“No, that doesn't work either. If your version of events were true, then Miss Riria would know that the person who set up the hidden camera – we'll call them 'X' – had seen her retrieve the cards. However, Miss Riria left the cards at the crime scenes. That's clearly contradictory. We would have immediately known they were her cards. The fact that Miss Riria left the cards at the crime scenes is proof that no hidden cameras were installed.”
Therefore, there was no possibility that the person who'd killed Yashiro had used a hidden camera to secretly watch Riria open the hidden compartment. In that case, there were a limited number of ways the culprit could have seen into her room. Or rather, there was only one. I said it.
“Then the only possibility is that the culprit looked into Riria's room through the window.”
Mitsumura laughed at my line. I'd thought I was helping with her deduction, but maybe my acting was a bit off. Mitsumura caught her breath and said “Kuzushiro is right.”
“The only way the culprit could have seen into the room is through the window.”
“But isn't that a bit careless?” Yozuki asked. “Why would she have taken out the playing cards, which were evidence of a crime, and risked being seen through the window?”
“No, it wasn't like that,” Mitsumura said with a shake of her head. “There was only one window in Miss Riria's room, and there was a curtain over it. It just so happened that there was a hole in the curtain, and if you went right up to the window, you could see through it into the room. I guess Miss Riria must not have noticed. The hole is small enough that you have to get very close to see through it. You couldn't have looked through from far away, even with a pair of binoculars. In other words, the only way the murderer could have seen into the room is to get close to the window and look through the hole in the curtains.”
After hearing that explanation, everyone nodded in agreement. “But...” Fenrir had a new question.
“What does that matter? The culprit approached the window and looked into the room through a hole in the curtain. That's how they knew how to open Miss Riria's smartphone case. That much I understand. But anyone could have gone to her window and looked into her room, no? I don't see how this leads us to the identity of the culprit.”
Mitsumura gave a gentle smile.
“No, it does lead us there.”
She stroked her glossy black hair.
“Because there is only one person who was able to look into Miss Riria's room. Naturally, that includes myself and Kuzushiro.”
Her comment put everyone on edge. There was only one person who could look through the window. That was the same as saying there was only one person who could have murdered Yashiro.
“But what do you mean?” Yozuki said, confused. “There was only one person able to look into Riria's room?”
Mitsumura shrank just a bit.
“I hate to admit it, but that wasn't entirely accurate. Strictly speaking, there was only one person able to look into Miss Riria's room while Miss Riria was present.”
Yozuki tilted her head again.
“I don't really get it.”
“It's simple, the culprit learned how to open the smartphone's case by watching her open it. That means there's no point in looking through the window while Miss Riria isn't present. For example, there would have been no purpose in doing so before her arrival at the hotel.”
Yozuki nodded. “So, it's important to think about what times Miss Riria was in her room,” Mitsumura said.
“When Miss Riria arrived in the House of Snow, she drank juice in the lobby for a while, then headed to her room for the first time. If memory serves, she got into a fight with Mr. Manei over a variety show questionnaire. As soon as she went to her room, it started snowing. It snowed heavily, and although it only lasted 30 minutes, it buried the whole garden in silver.”
That snow still hadn't melted, and it hadn't snowed once since.
“Snow had piled up outside the detached building where Miss Riria was staying,” Mitsumura said. “And there were no footprints near the building. Of course, that includes the space under the window. And that suggests a certain fact.”
Mitsumura explained to everyone.
“Since the snow fell, no one has come close to that window. If they had, they would have left footprints. And that means that since the snow fell, no one has looked through the window of Miss Riria's room.”
A smile spread across her face.
“Now, let's reconsider our information in light of this. The snow started right after Miss Riria went to her room. After the snow finished falling, no one could have gone to her window. In other words, the culprit looked through the window between when the snow started and when it ended. It's actually a very short window of time.”
Mitsumura's voice was calm and even.
“And the person with no alibi for that window is the culprit.”
The short 30 minutes between when the snow started and when it stopped. The person with no alibi for those 30 minutes was the culprit.
I remembered what had happened back then. When Riria left the lobby and it started to snow, almost everyone in the hotel was gathered in the lobby. The exception was Kanzaki, who hadn't arrived yet. The employees, Ms. Shihai and Miss Meirozaka, were also there.
There were only two people missing. It was just Riria, and them.
The person who came to the lobby about ten minutes after the snow started. Her silver hair had been wet with snow. And she'd given me a snow rabbit.
“That's why you're the only possible culprit.”
Mitsumura pointed at her.
“Miss Fenrir Alicehazard, you are the culprit.”
Fenrir's eyes opened slightly wider, then a soft smile appeared on her lips. She said only one thing.
“Correct.”
Her silver hair swayed slightly. Her confession brought a true end to the series of murders that took place at the House of Snow.
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