Attending ex-girlfriend's wedding, arresting the groom's officer on the spot

Lu Chuan's eyes swept around the freezer, and there were obvious pry marks and dragging blood on the metal surface. "Wang Shuai, retrieve all the surveillance cameras in the building, and focus on checking the entry and exit of people in the area where the freezer is located in the past week. Zhang Hui, go to the property management to check the usage records of the freezer. Such a large freezer cannot appear here for no reason."

Yang Lin and Yang Sen also arrived.

"Begin the investigation." Lu Chuan gave a brief order. Yang Lin and Yang Sen immediately put on professional gloves and goggles and started working.

Yang Sen half-knelt on the cold cement floor and took out a set of sophisticated fingerprint extraction tools from the investigation box. He first took out a multi-band light source, adjusted it to the 450-nanometer blue light band, and directed the light at a low angle to the surface of the freezer. Under the irradiation of the blue light, the metal surface of the freezer glowed with a faint cold light. He squinted his eyes and observed carefully, trying to find latent fingerprints that were difficult to detect with the naked eye.

“This multi-band light source can excite the fluorescent substances in the latent fingerprints. If the murderer simply wiped it, there may be residual substances that produce fluorescent reactions.

However, after a few minutes of careful searching, the surface of the freezer was still clean and there were no fluorescent spots.

Then, he changed to a magnetic powder brush. He held a special magnetic brush, dipped it in black magnetic powder, and gently swept it on the surface of the freezer. This magnetic powder can be adsorbed on the grease and sweat stains in the fingerprint pattern, thus revealing the outline of the fingerprint. "For non-permeable metal surfaces, magnetic powder brushing is one of the most commonly used methods." Yang Sen moved gently and skillfully, and the magnetic powder formed a uniform film on the surface of the freezer under the drive of his brush.

Unfortunately, as the powder moved, no fingerprint patterns appeared. Yang Sen frowned slightly and took out a bottle of 502 glue from the investigation box. This is to use the characteristics of ethyl cyanoacrylate. When 502 glue is heated and volatilized, it will react chemically with moisture, amino acids and other substances in the fingerprint, thus showing white fingerprint patterns.

He quickly built a simple fumigation device, poured 502 glue into a heating dish, and heated it with an alcohol lamp. White steam slowly rose and filled the freezer. "This method works well for fresh fingerprints. Even after wiping, as long as there is a trace of sweat left, it may show up." Yang Sen stared at the surface of the freezer, not missing any details.

However, after the fumigation process was over, the surface of the freezer was still as smooth as new, without any traces of fingerprints. Yang Sen was not discouraged and tried the silver nitrate development method. He prepared a silver nitrate solution and carefully applied it to the surface of the freezer with a cotton ball. Silver nitrate will react chemically with sodium chloride (a component of sweat) in fingerprints to produce silver chloride precipitation, thus revealing fingerprints.

"This method also has a certain effect on old fingerprints," Yang Sen said. But when the solution dried, there was still no harvest on the surface of the freezer. Finally, he even used vacuum metal coating technology, which is a high-end fingerprint display method that creates a contrast between the fingerprint pattern and the background by evaporating a layer of metal film on the surface of the object.

With the humming sound of the portable vacuum coating machine, a thin metal film evenly covered the surface of the freezer. Yang Sen held his breath and looked carefully through the observation window, but the result was still disappointing - the surface of the freezer was flat and smooth, without any signs of fingerprints.

"Captain Lu, the murderer is obviously very experienced in cleaning traces. We have tried all the conventional fingerprint extraction methods, but found nothing." Yang Sen took off his goggles, his forehead covered with fine beads of sweat. "Judging from the degree of cleaning, the other party may have used professional cleaning agents, and may even have used chemical reagents such as strong acids to treat it, completely destroying the fingerprint residue." On the other side, Yang Lin focused on the ground around the freezer. He half-knelt on the ground, holding an exploration light, shining the light on the ground at different angles. "The ground has been swept, there is only some dust, and the footprints are almost all from the thief who reported the case." Yang Lin said as he took a picture of the ground with a camera. "Judging from the distribution of footprints, the thief should have walked back and forth many times after entering the room. This freezer is surrounded by his footprints. And judging from the distribution, he panicked after finding the body. Apart from that, no signs of other people entering and leaving recently were found."

Lu Chuan frowned and looked around the room. The room was small, with nothing but a freezer and a worn-out safe. The walls and floors were ordinary, without any special markings or suspicious features. He walked over to the freezer and carefully observed the brand, model, and appearance details of the freezer, trying to find some clues, but found nothing.

At this point, Yang Sen turned his attention to the switch and lock of the freezer. "Although the fingerprints on the surface have been cleaned, these gaps and edges may be missed." Yang Sen took out a small brush and special reagents and tested them bit by bit. As time passed, his movements became more and more meticulous, and beads of sweat appeared on his forehead. However, the final result was still disappointing. No valuable clues were found in these locations either.

Yang Lin began to inspect the walls and corners of the room. He used a magnifying glass to examine the wall inch by inch, trying to find some scratches, bloodstains or other traces. In a corner of the room, he found a small tuft of fiber, which was gray in color and looked like a scrap of some kind of cloth. "Captain Lu, we have found something here." Yang Lin carefully collected the fiber and put it into the evidence bag. "Although I am not sure if it is related to the case, I will take it back for testing first. Maybe we can find something."

Lu Chuan nodded, his eyes falling on the body in the freezer again. "First, transport the body back to the autopsy room, and let Zhang Kai perform an autopsy as soon as possible to determine the cause and time of death."

Zhang Hui, Wang Shuai and others have already learned about the relevant situation from the building property management.

Yang Lin and Yang Sen continued to stay at the scene for a second round of investigation. They expanded the scope of the investigation to the corridor outside the room and the elevator room, hoping to find some clues that the murderer had overlooked. In the corner of the elevator room, Yang Sen found a small metal object that looked like a pendant on a keychain. He excitedly called Yang Lin, and after careful observation, the two carefully collected it.

"Whether it is related to the case or not, we must not let go of any small clues now." Yang Lin said. They searched the trash can in the corridor again, but found no other suspicious items except some food packaging bags and waste paper.

When they finished the on-site investigation and were about to return to the police station, the night had completely enveloped the city. The Chang'an Building looked particularly gloomy in the night, as if hiding countless unknown secrets.

In the forensic autopsy room, Zhang Kai has already brought the body back and is starting to perform an autopsy. (End of this chapter)