TPODN Chapter 55

“This is probably the most difficult part to understand. The only mediocre reason I can think of is that they might have been hired by someone with a motive. However, if, as we said earlier, the embezzled money was hidden in the chairman’s office, then the whole theory makes sense.”

“To get their hands on that money?”

“Why would the security guard know about the money?”

“I’m not sure, but it’s possible they accidentally found out while patrolling.” Hu Shi crossed his arms over his chest, looking troubled.

“It’s all just personal speculation.”

“However, although it’s not yet conclusive evidence, there are signs that the chairman’s office was broken into,” Wang Linfei said.

“Signs?”

“They’re on the books in the bookcase. I noticed it when I was looking at the robot experiment. The spines of some of the books had horizontal black marks. I guess it was from someone’s dirty hands touching the books after rummaging through something else.”

Lu Yao gasped in surprise.

“In that case, could we get fingerprints?”

“No, I didn’t see any patterns. Perhaps they wore thin rubber gloves or wrapped something around their hands.”

“…Anyway, until we hear about the locked-room murder method, we can’t make any further deductions.” Hu Shi’s attitude was still quite stubborn.

“Then, why don’t we go to the Maoyuan Building now?” Wang Linfei stood up.

“You go and explain the killer’s method.”

“To sneak into the chairman’s office, you have to pass in front of the security cameras in the hallway. The problem is, the images captured by the cameras are not only watched by the security guards, but also recorded intermittently. That is, there are two barriers: human monitoring and video recording. Just thinking about how to get through both at the same time puts me in a dead end.”

The three stood behind the monitors in the security room. In a corner of the room, a security guard named Wang Gang, who was not in the loop, stood by with a blank expression.

“But, if you don’t find a way to solve these two problems, wouldn’t the killer expose themselves?” Lu Yao asked, puzzled.

“That’s for sure. However, people and machines have different strengths, so it’s very difficult to deceive both with one method. In other words, the killer probably used a divide-and-conquer approach. It took you a while to realize this.”

Wang Linfei pointed to the surveillance screen.

“The first thing to solve is the on-duty security guard’s monitoring. Let’s assume for now that Hu Jianlei is not the killer. During the time of the crime, Hu Jianlei was sitting in this chair, watching the World Cup highlights on TV. Since the other three monitoring screens are also in view, it’s impossible for the killer to pass directly in front of the camera.”

At that moment, the screen showed Jiang Kefan passing through the corridor on the fifteenth floor. Even if you’re not staring at the screen, if a figure flashes across the screen like that, it should be impossible not to notice.

“However, a person’s attention will inevitably be interrupted at some point. No matter how focused you are, there will still be times when your eyes wander or you leave your seat. As long as you seize that moment, the killer should be able to stroll past the camera.”

“Seize that moment… how?” Lu Yao looked blank, as if lost in a fog.

“The only way you can think of is to monitor the security guard’s movements in reverse.”

Lu Yao suddenly understood. She recalled that when she first entered the security room, Wang Linfei had carefully examined the wall opposite the screen.

“As long as a large camera with wired transmission is installed in a corner of the security room, the killer can wait in the elevator hall on the top floor with a receiver with a built-in screen. Once the security guard makes a similar action of leaving the seat, or if their line of sight deviates slightly, they can pass in front of the camera.”

“As long as a repeater is set up in the inner stairwell, that won’t be a problem. Moreover, the stairwell is connected from top to bottom, and the most convenient thing is that there are also power outlets in the middle.”

“…But…” Hu Shi blinked repeatedly.

“Where should the hidden camera be installed?”

Indeed, there didn’t seem to be any suitable place to install a large camera on the back wall.

“Although I can’t be sure, I think there’s an ideal place.”

Wang Linfei tapped the large TV with his left index finger.

“From the perspective of monitoring Hu Jianlei’s line of sight, this is the ideal place. Moreover, if it’s placed here, it’s easier to deal with the power supply problem. As for shooting, it can be done through the small hole on the speaker.”

“In that case, maybe the camera is still inside?”

Hearing Lu Yao’s question, Wang Linfei shook his head.

“Impossible, I think it was disposed of long ago. The killer should have had plenty of time, since the crime scene was on the top floor. The police wouldn’t specifically check the TV on the first floor.”

“I see…” Hu Shi murmured.

“What if Hu Jianlei is the killer?”

“In that case, there’s no need to bother deceiving human monitoring. However, I still don’t think he’s the killer.”

“Is it because of hiding that envelope with 1000 yuan?” Lu Yao asked tentatively.

“That’s one of the reasons. Also, from my observation of Hu Jianlei, he doesn’t seem to have any knowledge of mechanical things.”

“Besides, if we consider another method, that is, if we want to avoid even the video recording, I still think Cui Xiao is the killer.”

“That’s right, I want to hear what method he used. Deceiving the security guard’s eyes is one thing, but not even being captured by the machine is like magic.”

Hu Shi muttered, expressing the same sentiment as Lu Yao.

“Then let’s go to the top floor and take a look.”

Before entering the elevator, Wang Linfei pressed the passcode with a matter-of-course attitude.

“I gave Lu Yao a hint earlier.”

Wang Linfei’s tone sounded like a teacher asking a student about their homework.

“Is it that thing about why we can’t see Santa Claus?”

“Yes.”

“I can’t figure out what that has to do with the case.”

Although unwilling, she could only accept it.

“…Um, is it because the killer’s actions were too fast?”

“Relatively speaking, that’s right. However, the more accurate statement should be that the monitoring party’s time is too short.”

“I don’t understand at all.”

“The meaning is very simple. The intermittent video recorder in the security room earlier properly recorded the surveillance camera images. The recording mode here is set so that one tape can store seven hundred and twenty hours of images, which means that each frame is six point zero one seven seconds. Therefore, as long as you grasp this interval, you can fool the camera’s recording and escape from the video unscathed.”

“Maoyuan International Group is still using such an old way of storing surveillance camera images. Isn’t it all cloud storage now?” Hu Shi said.

“That’s how they store the camera images. You saw it when you went to the security room last time. Hu Jianlei said that they will use cloud storage in the future,” Wang Linfei said.

“Huh?… But, in that case…”

As soon as the elevator door opened, Jiang Kefan greeted them. It seemed that the new chairman had issued an order for everyone to cooperate with the investigation.

“Thank you for your hard work.”

“Not at all, we’ll have to trouble you.”

During this time of exchanging pleasantries and interrupting the previous question, Wang Linfei had already walked quickly to the front.

“Please stop here.”

Wang Linfei pointed to the location from the lobby where they were about to enter the corridor. When the door to the corridor opened, although they could see the door of Minister Zhao Menglin’s office diagonally opposite, the corner of the secretary’s office became a blind spot for the security cameras.

“If the killer were to hide, they would probably hide here…. What is the frequency of the secretary leaving the office during the lunch break?”

The sudden question left Jiang Kefan at a loss, unable to answer for a moment.

“This… well, um, they almost never leave the secretary’s office.”

“The killer probably investigated this in advance as well. In that case, the only thing left to deal with is the surveillance camera. The killer used a small receiver to confirm the security guard’s situation, waited for the security guard’s eyes to leave the screen, and then quickly ran out after the next recording time had passed.”

Wang Linfei pressed the stopwatch button on his watch, jogged across the corridor, and then opened the door to Zhao Menglin’s office. He leaned his body slightly to slip in and gently closed the door from the inside. The whole process made no sound.

“My demonstration just now only took a little over five seconds.”

Opening Zhao Menglin’s office and poking his head out, Wang Linfei explained.

“In other words, even six seconds is enough for the killer.”

Jiang Kefan, who hadn’t heard the whole cause and effect, couldn’t help but stare blankly at Wang Linfei’s funny behavior.

“Six seconds is the minimum time required to get to the nearest Zhao Menglin’s office,” Hu Shi said, pondering with his arms crossed.

“The killer naturally knew that the doors of the Black Earth Chairman’s office, the General Manager’s office, and the Product Planning Department’s office were not locked. And the Director of Product Planning, Zhao Menglin, was in a deep sleep, so he wouldn’t notice anyone sneaking in. The killer went through the office of the Director of Planning, passed through the General Manager’s office, and arrived at the Chairman’s office…”

“Wait… wait a minute!”

Lu Yao finally caught a break to ask a question.

“During the recording, do the camera lights flash or show anything else?”

“No, even if you look at the surveillance camera, you can’t catch the exact moment of recording.”

“Then how do you confirm the timing of the action?”

“You have to record the intermittent recording cycle in advance in the security room.”

Hu Shi, who was standing aside with his arms crossed, kept shaking his head.

“But, it would be okay if the cycle was exactly six seconds, but now it’s six point zero one seven seconds, right? With a unit of one thousandth of a second, even with a stopwatch, it’s impossible to capture the exact cycle, right?”

Wang Linfei took out a rectangular box from his pocket, about fifteen centimeters by six centimeters in size. One end of it had a switch and a terminal for inserting a wire, and its appearance looked like an outdated portable radio.

“It won’t be a problem if you use this.”

“What is that?”

Lu Yao frowned.

“It’s called a tactile sensor.”

“A tactile sensor?”

It was a term Lu Yao had never heard of, but Hu Shi showed a look of realization.

“I know it? Team Hu.”

“Yes, a tactile sensor is like an extremely precise metronome that can beat at a unit of one millionth of a second. And at the front of this cable, there’s a vibration motor that’s the same as the one used in mobile phones. As long as it’s in contact with a part of the body, you can read the correct vibration rhythm. It’s like feeling the rhythm with your body.”

The killer used this instrument to measure the exact recording cycle….

Lu Yao was speechless.

Using the blink of the surveillance camera to completely disappear.

Just imagining it made her shudder at the killer’s cunning. Wang Linfei’s words about constructing a locked room by stealing time, which was extremely similar to riddles, could finally be understood.

“So that’s it. Does that mean that if the killer is one of the two security guards, they have the opportunity to access the recorder?” Hu Shi said.

“Yes. However, to steal time, you have to open the entire shell of the recorder and touch the internal timing parts. It’s quite difficult for a layman, but Cui Xiao majored in mechanical engineering.”

“But is Cui Xiao definitely holding a tactile sensor?”

“The Huangle District police said that they found Cui Xiao’s online records, and found that he had browsed websites that contained tactile sensor design drawings. In addition, there were also emails to and from friends discussing manufacturing methods.”

“…Based on these signs alone, it’s still impossible to use it as key evidence for conviction.” Lu Yao carefully chose her words and spoke cautiously.

“However, even if we only present the possibility of Cui Xiao committing the crime, it is also an indirect question of Mr. Zhao Menglin’s suspicion. In addition, as long as any evidence is found, it may allow the prosecutor to drop the charges.”

Lu Yao thought, this time it can finally be resolved.

The often unsolvable mystery of the locked room was finally revealed, and Zhao Menglin could finally be saved.

It was just that, at this moment, Lu Yao realized that he was not worth saving at all, and she felt extremely ironic in her heart.

At this moment, Wang Linfei received a call…

“Take a trip to the Huangle District Police Station!” Wang Linfei said suddenly.

…

Wang Linfei walked down the long corridor of the police station, always feeling a kind of indescribable awkwardness. All the people in front, behind, left, and right were from other departments, and even if he was a police officer from the Municipal Bureau, he would feel particularly strange.

Mou Ran turned his head suddenly, looking incredulous.

“Am I a weirdo? Why are you so excited?”

“It’s a conditioned reflex, from the moment I became a police officer, I get excited whenever I watch videotapes.”

“Nerve.”

Although Mou Ran scoffed, his expression did not carry a trace of anger.

Mou Ran, who was over one hundred and ninety centimeters tall, brought a great sense of oppression to those around him no matter which department he was transferred to. Because he didn’t care about his health at all, his whole body didn’t look sturdy at all, but his arm strength was far stronger than others, and coupled with his stubborn and cunning personality, almost no one dared to be his enemy.

“Wait here for a moment.”

Mou Ran opened the door to the conference room, which only contained cheap tables and steel chairs.

Entering the room, Wang Linfei waited leisurely. Since he had already come here, there was no need to rush.

In a little while, he would be able to reach a conclusion.

As long as he carefully watched the images on the videotape once, Lu Yao’s absurd reasoning of the three secretaries quickly changing clothes would probably be buried forever.

The problem lies in the method of using the tactile sensor.

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