The young man in the center of the classroom slowly straightened up, turned his back to Ye Yu and the three people at the door of the classroom, and did not say a word.

Ye Yu looked at the other party calmly, and in the case of being surrounded by the scene, the other party obviously had no possibility of escaping.

Sure enough, after a moment, the boy slowly turned around.

The childish face has no longer panicked at the beginning, and the body trembling due to nervousness has gradually calmed down, only to see the young man looking at Ye Yu and the others behind him expressionlessly, and that face is the second class leader Chen Xin once mentioned, and Lin Yutang's classmate - Liu Ziheng.

"You...... You...... Student Liu...... I didn't expect it to be really ......!? The head of the bald security section pointed to the handsome boy who had been arrested, and was so surprised for a while.

"Although it is unexpected, the culprit of the 'blood word incident' that happened in this classroom before is indeed this classmate Liu Ziheng." Ye Yu looked at the young man not far away and said calmly to the bald man. "Now that the evidence is conclusive, I think he's the prisoner you're looking for."

"Prisoners? I don't know what you're talking about. Liu Ziheng suddenly opened his mouth, but he flatly denied his accusations. I just left something in the classroom, so I came back and got it. ”

"Oh? What is there that you have to sneak into the classroom in the middle of the night to get it back? Ye Yu had been prepared for this and said unhurriedly. Then again, the thing you just put in your pocket is not very heat-resistant, and if you pinch it again, I'm afraid your body temperature will activate it immediately. ”

Liu Ziheng was startled, and then suddenly realized that he was holding the metal box tightly in his pocket because he was nervous, so he quickly pulled his hand out of his pocket.

"I ...... What does it have to do with you when I come to get something? Liu Ziheng stabilized his emotions and did not give in at all. And who are you? You're not from our school, are you? ”

"You just think I'm a nosy person." Ye Yu smiled and casually blocked the other party's question. "Except for the one in your pocket, the rest of the 'smoke generators' you want to recycle have all been removed by me in advance, and it's useless if you want to deny it, because these things are all stained with your fingerprints."

Liu Ziheng's face changed. looked at Ye Yu coldly.

"Your every move has been filmed since you infiltrated the school, if you want to quibble, please explain why you sneaked into the school in the middle of the night, and why you secretly installed a 'smoke generator' in this classroom?" Ye Yu smiled slightly and looked at the young man opposite indifferently.

“…… Hehe, I'll admit that I installed these 'smoke generators' because I just wanted to play a prank, and then I didn't think it was very good, so I wanted to take them down secretly. Liu Ziheng pretended to be calm and said.

"As for what you said about the 'Blood Word Incident'. The school has already investigated, and none of the students have the red paint used to commit the crime, and the blood letters appeared on their own overnight in the closed classroom, so what does this have to do with me? ”

"Of course it matters, because you're the only one who can do this, and I can even show you a complete reproduction of your 'game' right now." Ye Yu stared at Liu Ziheng and said word by word.

"This 'bureau' is complicated, but it is not complicated, and the most critical point is the 'crime tool' that writes these 'blood words'. I think the school started to check the wrong direction, because the words were not written with ordinary 'paint'. ”

Ye Yu said, taking out a small bottle of spray from his pocket. Signaling to the bald man beside him, the latter understood, and quickly turned around and took out a discarded wooden board that had been painted white from under the podium and handed it to Ye Yu. It's like you've been prepared.

Ye Yu took the wooden board and shook the spray in his hand, in Liu Ziheng's complicated eyes. A transparent powder was sprayed on the surface of the board.

"We used this white-painted wooden board as the wall of the classroom, and although the powder I sprayed just now was already attached to its surface, I couldn't see it at all, but ......" Ye Yu said as he turned the wooden board to the side of Xiaolu, who casually took out a can of hydrating spray from his bag and pressed it twice on the surface of the wooden board, and in the next moment, the change was quietly born.

The surface of the originally snow-white wooden board faintly appeared a touch of light red under the shroud of water mist, and then, the light red became deeper and deeper, gradually becoming as red as blood, and finally the word "leaf" was completely outlined, and the part on the wooden board that turned into blood red was the place where Ye Yu had sprayed powder before.

"It's impossible not to smell any paint you use, and the words on this wall are completely odorless, so I suspected at the beginning that there might be something else to this thing, and that's exactly what happened." Ye Yu put down the wooden board and said to Liu Ziheng, who had an ugly face.

"The powder I just sprayed on is actually a water-sensing reagent, which means that it is colorless and odorless when it is not wet, and when it touches water, it will show a deep red color. In order to control non-compliant warranties, many electronic equipment manufacturers put this water-sensing material inside the equipment to identify whether the equipment is damaged due to the user's artificial water ingress. The material is particularly adhesive, difficult to scrub and can change color according to a set humidity threshold that is irreversible. ”

Ye Yu cast his eyes on the white wall with mottled "blood characters" written on it, and continued to say to Liu Ziheng.

"If the words on the wall are sprayed with paint or other paints, apart from the smell I have just mentioned, the undried liquid paint written on the vertical wall will flow down a little bit because of gravity, but we do not see this at the edges of the words; If, as I just demonstrated, you can perfectly reproduce this situation on the wall if you spray it with a dry powdery water-like powder and then change color when it encounters water. Of course, if you disagree with this, we can sample the handwriting on the wall, and I believe the same conclusion will be reached. ”

Liu Ziheng still didn't say a word, but there was a trace of obvious shaking in his eyes.

"After the problem of writing the 'blood letter' is solved, we will discuss the problem of how to make it change color, which is the key 'how to meet water'." Ye Yu continued to analyze.

"We can see that there are several rows of smoke alarm sprinklers on the ceiling of this classroom, as long as smoke occurs in the classroom, the sprinklers in the corresponding area will automatically sprinkle water and sound an alarm, and the circle of sprinklers closest to the wall is less than three meters away from the wall, and the wall is basically within the coverage of the sprinkler sprinkler, that is, as long as this circle of sprinklers is triggered, the wall must be affected. As for how to make the corresponding smoke alarm nozzle spray water, it is the turn of this 'smoke generator' to appear. Ye Yu said to Liu Ziheng and raised the black metal little black in his hand.

"This 'smoke generator' is the kind of simple smoke generator with wireless remote control, which can be controlled without people present. In addition, I checked around, and this device was only attached to the row of desks closest to the wall, presumably you only intended to trigger the circle of smoke alarm sprinklers near the wall, so that the whole process of committing the crime was clear. ”

"Chief Ye, I'...... It still seems a little dizzy, can you put it simply? The successive messages seemed to make the bald man on the side a little too late to digest.

"To put it simply, Liu used this colorless water-sensitive powder on the white wall of the classroom to spray the words he wanted to write in advance, and then planned to use the remote control 'smoke generator' to disperse the smoke at a specific location, so as to trigger the designated smoke alarm nozzle in the classroom, and the water-sensitive powder on the wall turned red after touching the spilled water, so this 'blood word' was formed." Ye Yu explained, and then looked at Liu Ziheng.

"You've got a good plan, and you've carefully planned the location of the 'smoke generators', and I think you'd have done a few 'field tests' before to make sure the sprayed mist covers exactly what you're writing in, right?"

"I've heard that there have been a few cases of sprinkler failures in this classroom before, and all of them have been during non-school hours after school...... Could it be that he is doing 'experiments'? Shinoru suddenly remembered the situation mentioned by the bald man earlier.

I think so, but unfortunately, such a move became the direct fuse for his actions to be exposed, which I will explain later. I think what Liu is most confused about now is, how did I see the mystery of those bloody words on the wall? Ye Yu looked at Liu Ziheng, and his eyes flashed.

Liu Ziheng snorted lightly, noncommittal, and Ye Yu didn't bother to sell it, so he directly took out his mobile phone and clicked on a photo.

"This photo is the first scene photo taken by the security guard on the day of the incident, and we can see that in the corner of the white wall where the words are written, there is a sentence 'you will definitely pay', right?"

"There is indeed a sentence, we can also see the ...... on the wall now" Xiaolu glanced at the photo in Ye Yu's hand, and then looked up at the corner of the white wall not far away, and suddenly frowned. Wait a minute...... Something seems wrong! ”

"You can finally see it." Ye Yu smiled, waved his hand and dragged out a virtual screen from his mobile phone, showing a magnified photo in front of Liu Ziheng.

"In the photo, the sentence on the edge of the wall has no punctuation, and the handwriting is much lighter than elsewhere." Ye Yu said, stretching out his hand and pointing to the white wall in front of everyone. "Is there something more that you're actually looking at that place now?"

"'It's going to cost you!' …… One more exclamation point! "Even the bald man has found a problem." And now it's redder than the words in the photo, and it's also clear! ”

"That's because you've scrubbed it with water, and you've said before that you can't wipe off these words, and the more you wash it, the redder it becomes, isn't it?" Ye Yu broke through the mystery in one sentence. "In fact, the spray of water that day did not completely cover the row in the corner, so there was a strange phenomenon of 'exclamation mark' that was not in the first scene, but after cleaning the wall, it appeared."

"I see!" The bald man suddenly realized.

Of course, I am afraid that there will not be such a mistake in Liu's original plan, and after several previous on-site adjustments, as long as the plan he set is followed, the water mist should be able to cover these words perfectly...... However, he did not expect an unexpected event to occur, and this event was closely related to his previous 'field trial'. ”

Ye Yu looked at Liu Ziheng, who was pale, and said slowly.

"On the night of the accident, there was an 'accident' here." (To be continued.) )

PS: I'm sorry to update late, I've been so busy lately that I'm about to vomit blood...... (Support)