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

Chapter 430 Another case solved

Lu Chuan picked up the murder weapon and observed carefully: "The fingerprint lines on this murder weapon are blurred, and the edges are widely spread. It should be a kind of fuzzy indentation formed after the original fingerprints peeled off."

There are many ways to make fingerprints disappear. Some methods can make fingerprints disappear in a short time, while some methods can make fingerprints disappear for a long time.

No matter which one it is, it is enough to commit a crime.

For the fingerprints on the murder weapon, Lu Chuan preferred the fingerprint marks produced by peeling the fingerprints after being soaked in dilute nitric acid.

The other party must have done some research on fingerprints, and at least knows what concentration of dilute nitric acid can eliminate fingerprints without damaging the fingers.

It is impossible to simply look up information online.

You can find a method on the Internet to use high-concentration dilute nitric acid to eliminate fingerprints, but what is the specific concentration?How to match and deal with it?Soak for how long?
These cannot be known by simple online queries.

"Is there a warehouse at the logistics base where chemicals and other dangerous goods are stored?"

"This has."

Wang Chuanmin has been at the logistics base for a week and is familiar with every warehouse inside.

In fact, the entire logistics base is relatively remote, far away from the urban area. After the crime, the most likely suspect will most likely be hiding in the logistics base. Therefore, after the murder occurred, the Tianzhou City Criminal Investigation Detachment mainly focused on the staff in the logistics base to conduct the investigation. .

Wang Chuanmin himself has basically visited every logistics base warehouse.

In this regard, Qin Yong is much happier than Wang Chuanmin, because in the past year or so, many major and important cases have occurred in Haizhou City.

However, the detection was basically completed in a short period of time. Qin Yong had no chance or time to walk through each suspected scene one by one.

Wang Chuanmin had no choice. If the people below him couldn't help, he had no choice but to take action himself.

"Is there a laboratory?"

"Have."

"Captain Wang, let me use it to conduct an identification analysis on the murder weapon."

"Okay, I'll make arrangements."

Lu Chuan's identification and analysis of the murder weapon was not to re-extract the fingerprints on it for fingerprint identification.

The Tianzhou City Criminal Investigation Detachment's on-the-spot investigation was actually very good. In terms of fingerprint collection, although it did not reach Lu Chuan's level, there were basically no major mistakes.

It is very difficult to successfully identify and analyze such vague fingerprints on the knife handle. Even Lu Chuan would have to spend a lot of time and energy.

And whether the identification can be successful is not guaranteed.

Therefore, what Lu Chuan needs to do now is to analyze the residual substances on the knife handle to see if there are any chemical substances similar to dilute nitric acid remaining.

The murderer used chemicals to soak his fingers to make them peel off and make the fingerprints disappear. There would definitely be some chemical substances remaining in the skin, and testing would be able to prove whether such things exist.

If this is proven, then a focused investigation will be carried out on people who have been in contact with chemical substances in the park, and whose fingerprints are now missing, then there is a high probability that he is responsible for the crime.

The current investigation laboratory equipment of the Tianzhou City Criminal Investigation Detachment is relatively complete. Although it cannot keep up with the equipment equipped by the Haizhou City Criminal Investigation Detachment at this stage, it is much better than the previous equipment in Haizhou City.

Extracting the residue from the knife handle is as simple as soaking it in an extraction solution.

But this kind of extraction is a one-time operation, which means that if Lu Chuan extracted the substance on the handle of the knife this time, it will be very difficult if someone wants to extract it next time, because the amount of residual substance is very small, and it will basically be gone after one lift. there is none left.

As for proving the existence of nitric acid, it is simpler. Just put the extracted solution into a test tube and heat it directly.

When nitric acid is heated, brown-red gas will be produced, which can turn anhydrous copper sulfate blue.

It's a very simple chemical reaction that even junior high school students can do.

The experiment ended quickly, and the results verified Lu Chuan's conjecture.

Logistics warehouse, Tianhong Chemical Materials Storage and Transportation Company. "This is the only logistics company among all the warehouses in the northern suburbs logistics base that transports and stores chemicals."

Outside the park, Wang Chuanmin, Lu Chuan and others have arrived.

"Let's check first, especially if there are any workers who have injured their hands recently. We should focus on the investigation."

Wang Chuanmin didn't expect that Lu Chuan would give out clues so quickly.

This company was also within the scope of the investigation before, but no abnormalities were found at that time.

All police forces are now here. As long as the other party is really there, there is no possibility of escaping.

However, contrary to expectations, after questioning one by one among the 32 people in the company, no one had any injuries to their hands.

After Lu Chuan learned the result, he frowned.

If you look at it this way, it’s not quite right.

Use dilute nitric acid to soak your fingers. If the concentration is wrong, serious consequences will occur.

Dilute nitric acid is a highly volatile chemical substance. It does not mean that the more dilute the concentration, the less destructive and corrosive it is. On the contrary, low-concentration dilute nitric acid is more corrosive at a certain critical value.

"Check again, Captain Wang. I suggest checking people who have resigned from this company before. After dilute nitric acid corrodes fingerprints, it takes about three months for the skin to grow back."

"Investigate the information of all employees who have resigned within three months!"

"Okay, I'll make arrangements."

The human resources department of Tianhong Company quickly obtained the information of those who resigned within three months.

There are three people in total.

"Our company is relatively small, and the turnover of personnel is not particularly large. These three people all left because of family matters."

"Zhang Zicai, Liu Gensheng, Wang Yong."

These are the names of the three people who resigned.

"Check this first, Zhang Zicai."

After Lu Chuan read the resume information of the three people, he first targeted Zhang Zicai.

Among the three people, Liu Gensheng drives a transport truck and is a driver. Wang Yong is a logistics manager responsible for cleaning the factory area and is a cleaner.

Only Zhang Zicai is a warehouse manager. He is the only one who is most likely to come into contact with chemical substances.

And this person's education level is also the highest among the three. The other two have primary school education, and only Zhang Zi has a high school education.

high school student...

As long as you are not particularly bad at learning, it is relatively easy to master the preparation of dilute nitric acid.

With a target and a direction for solving the case, Wang Chuanmin also arranged three groups of people to conduct follow-up investigations on the three people who resigned.

This is the advantage of having more people. Lu Chuan had his reasons for focusing on investigating Zhang Zicai.

But if there is no shortage of manpower, the three people can investigate together.

However, Zhang Zicai invested more force here.

Liu Gensheng, after resigning, still worked as a driver for a company outside the park, but he drove a car.

"Driving a transport truck often requires staying up late. Although the salary for driving a transport truck is higher, my body couldn't bear it as I got older, so I quit my job there."

(End of this chapter)