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

Chapter 484 is not logical
Extracting DNA information substances from blood is simpler than extracting DNA information substances from other carriers such as bones, hair, and dander.

Most of the substances in blood are water. Extracting genetic material means stripping out other impurities. This process is called purification of genetic material.

There are some differences in the purified substances for the extraction of DNA substances on different carriers.

To extract DNA genetic material from blood, purified substances are the simplest. However, to extract genetic material from bones and other carriers, the purified substances required are slightly more complicated.

The purified substances used by the criminal investigation detachment have fixed ingredients.

Different carriers and what purification substances are used are specified.

Except under extremely special circumstances, detectives currently investigating are not allowed to prepare purified substances for DNA extraction.

When Lu Chuan was in college, his tutor told all the students when he first came into contact with DNA material extraction.

The fundamental reason is the issue of legality.

The criminal investigation major is a very principled major.

Whether the conclusions drawn from some experiments conducted by the current criminal police can be used as judicial evidence depends on whether the process of extracting physical evidence is legal.

The legal process here includes both the process of obtaining physical evidence and the process of handling the physical evidence.

There are corresponding regulatory requirements for the handling of physical evidence by the criminal police at present, and all behavioral processes must meet the requirements before they can become judicial evidence.

Yang Sen and others have been working for more than ten to twenty years and are very familiar with these standardized process requirements.

"The DNA information of three people has been isolated."

The DNA material of three people has been isolated from the blood stains wiped by the murderer, and Yang Sen is still continuing.

If the murderer left his own bloodstains at the scene, then theoretically, the DNA information of five people can be isolated from where the murderer wiped the bloodstains.

Four of them should belong to the four victims, and the other should belong to the murderer.

Yang Sen is doing DNA isolation at the location where the blood stain was wiped, while Lao Bai and Liu Guodong are doing DNA information extraction from the other four people.

After comparing the two sides, the murderer's DNA data can be obtained.

Lu Chuan is also busy here. The murderer left footprints at the scene, and Lu Chuan is making a footprint identification and analysis report.

Although Lu Chuan had already determined the general physical characteristics of the murderer at the scene, issuing an identification analysis report and dictating it were different.

The footprint identification report must have judicial effect, so the data analysis of the footprints is more important.

This is not something Lu Chuan can say based on experience that others can believe. It needs to be supported by enough data.

Another point is the on-site fingerprint extraction.

The crime scene was messy and there were residual fingerprints in many places. The murderer did not clean up the fingerprints at the scene after committing the crime.

Wiping fingerprints was actually the most time-consuming task for the four of them at the scene just now.

Lu Chuan roughly reconstructed the crime scene based on the blood stains at the scene. The murderer should have committed the crime relatively quickly and did not stay at the scene for too long. The murder weapon should have been taken away, and one of the pillow towels on the bed was taken away by the other party.

The things that could theoretically leave fingerprints were gone. In other places, the possibility of the murderer leaving fingerprints was actually not high.

Lu Chuan's current focus is on fingerprint identification extracted from the door.

Judging from the time of death of the victim, the murderer committed the crime between 3 and 4 o'clock in the morning today.The fact that the murderer was able to attack the four deceased persons while they were sleeping meant that the opponent should have the key to the room.

Then, if the murderer did not wear gloves when he opened the door, he would most likely leave fingerprints.

The action team responsible for the investigation also concluded that an acquaintance committed the crime.

The environment at the crime scene was relatively complex, and the entire building was being rented out by the landlord. The fact that the murderer was able to accurately touch the victim's home showed that he was very familiar with the situation in the building.

This is also one of the important reasons why Wang Junshan was included as an important suspect. Last year, he lived with Zhang Xiaotian and must be very familiar with the environment here.

And since they have lived together before, it is not surprising that they have the key to the room.

While the current investigation was progressing, Wang Changjiang and Shen Yan also began to conduct autopsies on the bodies.

The cause of death is relatively easy to determine. All four deceased died from the same sharp weapon, chopping the neck, stabbing in the chest and abdomen, resulting in massive blood loss and death.

"There were signs of a struggle at the scene, but why didn't the neighbors notice the cry for help?"

Shen Yan was a little strange.

Judging from the traces at the scene, there were two male deceased. It was possible that the carotid artery was damaged in the first place, resulting in loss of combat effectiveness. But what about the other two women?
The two female victims showed obvious signs of struggling with the murderer. Why did they not call for help during the struggle?
The soundproofing effect of the rental house was not good. If the two female victims shouted for help, people around them should be able to hear it.

But the reality is that no one called the police during the entire process, and judging from the results of the investigation, no one discovered that the family was murdered.

"Take it back and do the dissection."

Shen Yan was not a front-line investigator. Although she had some questions, she did not go into details. Autopsy was the job of the forensic doctor.

Although there were four corpses at the scene, the work of examining the corpses was relatively simple. The cause of death was clear, and the time of death was also relatively clear. The forensic doctor mainly did some toxicology analysis to see if there were any other special circumstances.

Shen Yan ignored the problem because she was a forensic doctor, but Zhang Hui and others, as frontline criminal investigators, would not ignore such obvious doubts.

On the way to arrest Wang Junshan, Zhang Hui and others were discussing the case.

"Brother Hui, there's something wrong with the investigation situation in the building..."

"Huh? Where are you referring?"

"Judging from the time of death, the victim was killed between 3 and 4 o'clock this morning."

"At this time, it is less than an hour before dawn. Several renters living in the building work in the vegetable market selling vegetables."

"It stands to reason that they should have gotten up earlier, so why didn't they hear any noise?"

"There are also signs of a struggle between the two female victims and the murderer at the scene. The two female victims were not killed immediately. Didn't they call for help during the fight?"

"The soundproofing of the rental house... When we were investigating next door to the crime scene, we could hear Liu Guodong and the others investigating the scene next door. The soundproofing was so bad that the neighbors didn't notice the sound of fighting?"

"It's not logical."

Zhang Hui nodded. There were seven households in the building, one of which was right next door to the crime scene. The remaining six households were either upstairs or downstairs, but they were not far apart.

Although 3:00 to 4:00 in the morning is the time when people sleep more peacefully, but as Lao Zhao said, seven households didn't hear a sound at all?
why?
Two reasons, either there was no sound at the crime scene, or...these seven families were lying.

(End of this chapter)