Chapter 25: Crazy Rubbing

After wiping the cup, wipe the glass, after wiping the glass, wipe the mirror, wipe the smooth one first, wipe the rough one, wipe the rough one first, wipe the fine one, wipe the fine one first, wipe the soft one, wipe the hard one last...

Investigation work, from a big perspective, is of various kinds, but from a detailed perspective, it is all small and trivial things.

The police say that case detection is the result of resources, which can be reflected during the on-site investigation.

For example, wiping DNA and fingerprints, laymen often think that as long as the suspect leaves DNA or fingerprints at the scene, he will be found by the on-site investigators, but in fact, there is no advanced instrument in the world that can accurately detect all fingerprints and DNA within a certain range.

For example, fingerprints are first divided into three types: explicit, plastic and latent. The first two can be seen, and the latter, as the name suggests, requires certain means to be seen. And these means must also adopt different solutions according to the different materials of the location of the fingerprint. Or powder, or pipeline, or smoke, or chemical reagents, or different chemical reagents, or different chemical reagents...

In view of this, the on-site investigation or trace detection personnel, in order to obtain a fingerprint, first need to determine where the fingerprint may exist, and then observe. The observation method can be done with the naked eye with the help of light or angle, or by breathing on a smooth surface, or by using a magnifying glass or ultraviolet light. After the location of the fingerprint is determined, the fingerprint is extracted by brushing powder, or iodine fumigation or silver nitrate or other reagents are used for chemical extraction.

Therefore, if there really is a Spider-Man crawling over the ceiling, the person doing the on-site investigation will most likely not find the fingerprint on the ceiling.

The trouble of DNA is even worse than fingerprints.

After all, fingerprints can be seen. DNA can be seen sometimes, and sometimes it can only be guessed.

For example, it is common to extract DNA from the victim's toothbrush. The police who do the extraction naturally cannot see anything. It is nothing more than guessing that there is a high probability of DNA on the toothbrush.

If we change to objects with a lower probability, such as shirts, bed sheets and other underwear, or water cups, porcelain bowls and other items, whether there is DNA on them is completely based on guessing.

The ability to do on-site investigation is very clear at this time. Some on-site investigations think from the perspective of the suspect, guess the other party's actions and sleep, so as to find possible clues and brush powder in an orderly manner; some on-site investigations just pack up shirts, bed sheets and the like, or just cut off a few pieces at random, regardless of whether they are really useful...

However, in general, the more people involved in the investigation, the stronger their ability, and the more time and energy they invest, the higher the probability of finding clues and evidence.

Jiang Yuan's operation method is extremely strong in Wang Zhong's opinion, but he thinks it is more appropriate during the murder case. If it is a theft case, it is almost impossible to operate like Jiang Yuan. The cost of making a tube of DNA is less than 100 yuan for the reagent alone, and the number of times it can be done per unit time is even more limited. It is very likely that you can't get in line even if you have hair on the biological specimens...

"Let's wipe the bathroom again." Jiang Yuan cleaned the bedroom, and it was already dark.

Wang Zhong patted his head and pointed to a large box of evidence bags, saying, "Why don't we come back tomorrow? There are hundreds of them. If we give them all to the lab, they will go crazy."

Jiang Yuan explained, "More than half of them are probably not DNA, so there is no need to use reagents. The murderer did it too cleanly. Look at the bedroom, fingerprints in many places have been wiped clean. In addition, the victim bleeds so much, the murderer must have spent a lot of time in the bathroom, rinsing the rag, or even taking a bath and washing clothes. The probability of DNA being found in the bathroom is very high."

"Xiao Hu and the others also guessed so, and they wiped it carefully." Wang Zhong said.

"It's still too rough." Jiang Yuan paid attention to the operation of Xiao Hu and others when dealing with the corpse, so there was nothing to be afraid of at this time.

"Well... okay, I'll work overtime with you today." Wang Zhong didn't think so before, but now he began to realize that the level of the several on-site investigators in the team was indeed a bit casual, just like his fingerprinting skills. The best evaluation is probably "useful".

In the past few hours, the missed fingerprints found by Jiang Yuan may not be able to solve the case, but it has proved that he and Lao Yan are not "useful" enough.

"That..." The old man at the door couldn't stay any longer and said, "We have to go home for dinner."

"Just sign and go back." Wang Zhong didn't expect the old man to stay for long. Witnesses are like this, either they don't want to get involved, or they walk around and talk nonsense, or they don't have patience.

Wang Zhong didn't think of educating others. He directly took the on-site investigation record, turned to the signature page, asked the two to write their names, and opened the door to let them out, only reminding: "What you saw and heard today, you can only say when the court or relevant departments ask, and you can't leak it out at other times, otherwise you will be held criminally responsible."

The two old men went out and nodded impatiently and said "I know, I know".

Wang Zhong nodded as if it was normal, closed the door and went back to the house, continuing to help Jiang Yuan wipe the DNA and fingerprints.

The lighting in the bathroom was not good, so it was more difficult to wipe.

Jiang Yuan wiped very hard.

Crime scene investigation LV4 not only improved his operational ability, but also his cognitive level.

All kinds of criminal theories actually illustrate a truth: the longer the criminal stays at the crime scene, the more things he does, and the more flaws he reveals.

For example, the murderer this time seemed to have cleaned up the crime scene carefully, and even calmly took a shower, but from Jiang Yuan's understanding, this only reflects the murderer's amateurism and arrogance.

The current DNA technology can even identify identity information from sweat. It is absolutely impossible to clean the bathroom flawlessly in a short time. If it is really a little more professional, at least the bathroom should be covered with plastic, and then the plastic can be taken away directly, buried or burned, and the physical evidence information leaked will be much less.

However, in that case, there will be traces of tape or sticky at the scene...

Jiang Yuan is actually not sure where the murderer's DNA can be wiped. He is just young, has good physical strength, and wipes like crazy.

Wipe.

Wipe...

Jiang Yuan is still in the excitement period of a novice. He has just obtained the crime scene investigation LV4 skill, and the scene he has actually investigated is the one in front of him. Naturally, try and practice as much as you can.

Among the skills of current survey, technique is of course very important, and meticulousness is indispensable. On the other hand, physical strength, energy, and concentration are the key to further improvement. It's like Xue Huaiyi fell out of favor with Wu Zetian, because he was experienced and improved in skills, but was disliked? Obviously not. In the same way, the Zhang brothers would not fall out of favor because of their youth, recklessness, and inflated impulses.

Wang Zhong lacked a lot of the above, but although he was a little tired, he was also supported by Jiang Yuan.

Jiang Yuan especially wiped the ceiling and corners of the bathroom carefully.

The more he went on, the more careful and confident he was.

This house did not separate dry and wet areas, but the area of ​​the bathroom was small. When taking a shower, the probability of water splashing on the walls and ceiling was not low, and it was even more impossible to clean it thoroughly in a short time. The only problem is whether DNA can be wiped. The bloodstains may have been washed away or destroyed, but if he wants to wash away all DNA traces, this person is probably still an amateur.

Ordinary people, who kill people unplanned, normally do not learn relevant skills in advance. Even if they learn, they may not work hard and seriously, and they may not learn well. Then it is natural that they will be caught by the police who work hard and learn well.

At night.

Jiang Yuan and Wang Zhong dragged their bags back to the police station and went straight to the DNA laboratory.

Nowadays, there are more and more cases of using DNA to solve crimes directly, and the investment of the police in DNA laboratories is also increasing. Even Ningtai, a poor county, has built a DNA laboratory under the guidance of various subsidies and policies and in accordance with the standards given by the ministries and commissions.

This is also the money-eating unit of the police station. The laboratory of a total of three people devours more than 10% of the police station's funds every year, and it has to increase from time to time.

However, unlike Wang Zhong's expectations, the DNA laboratory just silently accepted the piles of evidence bags without raising any objections.

They did not even carefully check and pick the biological samples sent by Jiang Yuan and Wang Zhong.

"How come old Qian from DNA has become so easy to talk to?" Wang Zhong followed Jiang Yuan to the forensic office and started talking.

In the forensic office, Wu Jun did not go home either. Like most criminal police officers, he sat in the office and sorted out the information he had collected during the day. Standing up and rubbing his eyes, Wu Jun slowly said, "In the afternoon, the captain was still angry. The problem now is that there are no clues. The DNA laboratory is eager for you to send the samples to avoid being idle."

Jiang Yuan was amused: "Does not working at night count as doing nothing?"

"The captain has not gone home." Wu Jun said, "If they can't find anything, they will go to re-investigate themselves."

Wang Zhong looked at Jiang Yuan, clicked his tongue twice, and said, "It's useless for them to go. As for their current investigation level, I'm not saying that ordinary cases are just for nothing..."

Wu Jun interrupted Wang Zhong: "Do you think they don't know it themselves?"

"Uh..." Wang Zhong was speechless and returned to his office silently.

Jiang Yuan was quite satisfied. He packed up and laid out a camp bed in the office.

Until the noise, the police officers who had been up all night started to quarrel.

"The DNA match found a person, Captain Liu took people there." Wang Zhong was the first to rush into the office, with secretions hanging from the corners of his eyes.