Chapter 79 The peaceful atmosphere
Afternoon.
The sun shines in the yard, creating a peaceful atmosphere.
There are only six criminal police officers, working hard and brilliantly to send seven people and more to prison.
"Magnetic powder will do."
"It's better to use ultraviolet light first."
"This... Ninhydrin."
Jiang Yuan stayed at the crime scene for several hours and easily gained the right to speak at the crime scene.
Some of them were a little uncomfortable at first, but gradually they became familiar with Jiang Yuan's style of doing things.
The crime scene at this time is like a workshop or an office. The presence of strong technical people will eventually lead everyone to the same or similar technical indicators. Otherwise, the work will not be done.
In terms of fingerprints alone, the fingerprints scanned by Ningtai County investigators were for Yan Ge and Wang Zhong. The requirements for the latter two are roughly clear and accurate. If you can't do it, you won't say much, just think that you are incapable.
Jiang Yuan's requirements in this regard are extremely different, because he knows how far he can achieve it, so for the fingerprints used for comparison and the fingerprints that need to be stored in the warehouse, Jiang Yuan's requirements are naturally higher.
However, the most critical thing is that Jiang Yuan can give a clear plan and get clear fingerprints.
Several current police officers have really never enjoyed such "teaching" after leaving school.
Just like ninhydrin reveals fingerprints, this should be the most commonly used technique, including in books and classrooms, as well as many crime scenes.
It is a chemical reaction, and the mechanism itself is relatively complex, but in terms of effect, the ninhydrin method can clearly reveal latent fingerprints on light-colored papers, tickets, and even wood products. This is a very useful and awesome solution.
But in real crime scenes, criminal police rarely use this method.
It is no exaggeration to say that for the vast majority of on-site surveys, the most commonly used, most commonly used, or even the only solution used is the powder method.
"Going all over the world with one brush" is the daily state of most criminal investigations.
No need to change the powder type.
The people doing the spot survey today are all technicians from the Criminal Division Squadron. Occasionally, they will still use ninhydrin and 502 fumigation. But today is a state of full deployment, so there are so many technicians coming out.
Normally, many minor cases are scanned for fingerprints by criminal police officers and police officers from the police station and put into storage on the spot, and many of them have no idea how to use ninhydrin and 502 fumigation.
In fact, because they are used sparingly, the technicians of the criminal squadron are not very skilled in using ninhydrin and 502 fumigation.
This is also very easy to understand. If a person takes the same route to work every day and can reach the work smoothly, then unless something unexpected happens today and the previous route is really impossible, why should it be changed? What about other routes?
This is the case for technicians in Ningtai County. Any fingerprints that can be scanned with powder must have been scanned with powder.
No one even bothered to change the type of powder.
Unless it is a non-smooth surface or textile, and the fingerprints cannot be revealed with powder, and the fingerprints are important, technicians will use ninhydrin.
This is equivalent to wind and rain. As long as the road is not washed out or blocked due to emergencies, there is basically no need to change the road.
However, in the past, it was Yan Ge and Wang Zhong who needed to analyze fingerprints, but now it is Jiang Yuan.
Jiangyuan is like an organization that requires working hours, and an organization that requires constantly reducing commuting time. For on-site technicians, if they want to meet this standard, it becomes very important to choose the appropriate path.
Of course, the important thing is that everyone is also willing to reduce commuting time, or in other words, is willing to cooperate with Jiang Yuan to improve the quality of fingerprints in the database.
In criminal science and technology, this is the secret book of martial arts. It is not only the capital to settle down, but also a tool for self-improvement. Everything is done, and most people are still willing to do it well.
And if you want to do anything well, it is actually a bit difficult.
Just like ninhydrin, anyone who has studied in the police academy for three or four years can say "I am familiar with this".
But when you really ask: "Which ninhydrin formula do you usually use?" 80% of people will be confused.
Only technicians like Wang Zhong, who have really used ninhydrin, can easily come up with the formula of 1g ninhydrin and 100g absolute ethanol, and said: "We used to use acetone more, but now the management is stricter. It’s not easy to take out too much acetone…”
Jiang Yuan gave a ruthless response: "It is recommended to add ether."
"Hey, do you want to add ether to the formula? Add... 60g?" Wang Zhongxian thought about the formula, but it turned out that it was not very clear.
Jiang Yuandao: "We need 2g of ninhydrin, then add 5g of absolute ethanol, and then 5g of ether. Because the latent fingerprint we are trying to do now is on a colloidal object. After adding ether, it will be clearly displayed. More. The 1:100 ethanol formula you just used is fine when used on paper, but the effect will not be good when used on colloidal objects."
"You said that with my brain, I have learned the recipe before." Wang Zhong patted his forehead. He had learned it, but he had only used it for so many years and could not remember the plan at all.
As Wang Zhong spoke, he prepared the ninhydrin on the spot and swiped it onto a brown paper bag.
Jiang Yuan moved his lips but made no further request.
The color development time of ninhydrin is one to two hours, but there are other ways to speed it up. However, there is still plenty of time now, and Jiang Yuan does not need to be picky.
No one asked any more questions, so Jiang Yuan found a rough object and started doing it himself.
The inherent knowledge of criminal police is to find fingerprints on smooth objects. In other words, given everyone’s technical level, it is not easy to figure out fingerprints on smooth objects.
Jiang Yuan took out a glue gun from the discovery box.
I saw him sprinkle the powder on the LV presbyopia leather bag where fingerprints were to be extracted, then raised the glue gun, sprayed out a thick gel-like liquid, and heated it with a hair dryer.
Several surveyors nearby were stunned.
"Do we still have this equipment?" The head of the current surveyor was filled with questions.
"I found it in the warehouse." Jiang Yuan held up the glue gun and started walking around, adding: "I guess I bought it as a set."
"That's for sure. They're all bundled now..." Xian Kan looked helpless and suddenly felt like he knew nothing about the situation in the bureau.