1995, Starting as a Criminal Investigation Expert

Li Shu then carefully reviewed the numerous documents in the system.

First, it's a non-permeable fingerprint carrier, and then it's a sweat fingerprint.

Or to be more precise, it's a fingerprint made up of sweat and oil.

The composition of this fingerprint is 90% water, mixed with inorganic salts, amino acids, oils and other substances.

The moisture will evaporate, and after 14 years, the amino acids will have long since degraded.

However, substances like oils and inorganic salts, which are not easily degraded, still have a chance of remaining even after so many years if stored in a sealed container.

Currently, there are only a few methods for detecting latent fingerprints, depending on the carrier.

Non-penetrating powder, 502 fuming.

For the permeation carrier, such as paper, ninhydrin, silver nitrate, or iodine fumigation can be used.

Li Shu asked.

When fingerprints were extracted in 81, the method used was to scan for fingerprints.

At that time, there was no method for using 502 super glue for fumigation.

This method was invented in 78, and it wasn't until 83 that the journal "Criminal Technology" published a related report.

The transfer process using adhesive tape may damage fingerprints, but there will still be slight residue.

This is the basis for Li Shu's belief that secondary extraction is possible.

The 502 fuming technique is a one-off deal; if this method had been used back then, the internal components of the fingerprint would have been destroyed long ago.

There are actually quite a few methods in the system for dealing with this situation.

However, after conducting research, Li Shu believes that at this stage, the only usable method is VMD, vacuum coating technology.

This thing has a fancy-sounding name, but it's actually just an industrial coating process.

In the 1970s, Scotland Yard in the UK was the first to use this method to extract sweat-induced signals from non-permeable carriers.

This technology was introduced to China in the 1980s.

In 82, they produced the first high-vacuum coating machine in the country.

Its working principle is similar to the method Li Shu previously used to collect fingerprints from frozen corpses.

In a vacuum environment, gold and zinc are evaporated sequentially, and the fingerprints are left to settle in the papillary lines and furrows, creating a contrast that reveals the fingerprint.

The system describes this method as being far superior to 502 smudging for old fingerprints.

There are clear cases. In 98, this method was used to extract fingerprints from the plastic bag that had wrapped a body 16 years earlier.

The method was good, but China's industrial technology was relatively backward in the 1980s.

The coating machines produced were expensive, complicated to operate, noisy, and had problems with wastewater discharge, so they were eventually phased out and abandoned, and never gained widespread adoption.

According to the timeline of data, this technology was not reintroduced until the beginning of the next century, starting in 08.

Li Shu immediately contacted Zhou Xuewen to inquire whether Songpu had a coating machine.

This technology has always been experimental and has not been widely adopted.

However, if it's just an experiment, the cities most likely to have it domestically are Ankyo and Matsuura.

"High vacuum coating machine? How do you know about that?"

Zhou Wenxue never expected Li Shu to be able to say this.

This method has never been promoted as a formal approach, so it's impossible for it to be taught in police academies. So where did Li Shu learn about it?

Most importantly, Matsuura actually has it.

Zhou Xuewen led Li Shu to the warehouse and explained, "At that time, the ministry took the lead in finding two companies for this kind of machine. One was from Kang Province, and the other was our Songpu Machinery Factory."

"Only a few units were produced in total, and we were given one in Matsuura. The department's idea was for us to figure out how to use it and accumulate some experience."

"But this thing is not easy to use. The operation method is too complicated, and the craftsmanship is not up to standard. It takes a long time to vacuum."

"There are also requirements for the deposition time of gold and zinc. You have to figure it out by trial and error. If you don't do it properly, you can damage your fingerprints."

"And think about it, this stuff requires evaporating pure gold, which is very expensive. Just then, the 502 fuming method was introduced, and it was both cheap and effective."

"So this thing was gradually phased out and abandoned. If you hadn't brought it up today, I would have forgotten about it long ago."

He arrived at the warehouse door.

This warehouse in front of us stores some old items that have been disused for a long time.

The key I had wasn't right, and after searching for ages, I couldn't find it anywhere, so in the end I had to pick the lock.

When it was opened, dust flew everywhere.

Zhou Xuewen was a little confused, having no idea where the item was.

They called for more people to search, and after a long time, they finally found this large wooden box hidden under some miscellaneous items in a corner.

"Li Shu, are you sure this thing will work?" Chen Shengkang came over after hearing the news.

Li Shu nodded: "Anyway, the information I saw said that it works very well for old fingerprints."

When asked how he learned about this method, Li Shu claimed that a relative had access to it overseas.

Because of his interest in criminal science and technology, he often asked relatives to purchase the latest information from abroad.

That's how I learned about this method.

That's how they managed to get by.

It's quite large, well-made, and weighs several hundred kilograms.

Because of the high production cost, it was packaged very well when it was sealed, and now that it has been opened, it is in perfect condition.

Li Shu gestured silently, feeling that he could put the air vent grid into the instrument.

This thing will work.

Li Shu looked excited and said, "Director Zhou, I think we can really give it a try. The existing fingerprints are insufficient, but I believe there must have been very faint latent fingerprints left at that time, which might be able to be revealed."

Zhou Xuewen hesitated.

The main problem is that nobody knows how to use this stuff properly, and like super glue, it's a one-off deal.

If it works and succeeds, great; but if it fails, the original physical evidence will be destroyed.

Li Shudao said, "That's easy, let's try it out first."

And there's one more thing.

Back in the 1980s, the manufacturing process for this product was not up to par.

Now, more than ten years later, thanks to the introduction of the Volkswagen Santana, Matsuura has accumulated a wealth of process technology and is now fully capable of making this coating machine even better.

Zhou Xuewen and Chen Shengkang discussed it and agreed.

Let's try it first, and then we'll talk about it.

The first issue is to confirm that the instrument is still usable.

After being powered on, the vacuum pump was not running smoothly and was leaking air.

That's easy, just contact the original manufacturer directly.

The workers who produced this instrument ten years ago are still here.

Using the old machine and the new process, the repair was completed in just two days.

The system information is very detailed.

There is a principle behind this method, and there is a lot of research data on different carriers.

You may not have the operating instructions for this old-fashioned instrument, but you do have more advanced ones. You can refer to them; there shouldn't be any problem.

Li Shu personally conducted the experiment.

Using the same galvanized sheet material, before pressing his fingerprint, Li Shu first wiped his oily face, which was greasy from staying up all night.

Seeing Zhou Xuewen looking at him curiously, Li Shu said, "Chief Zhou, whether this method will work depends on whether the suspect smeared something on his face when he hid it."

The physical evidence had been sealed for 14 years, and only trace amounts of grease remained.

Normally, there is very little oil in sweat fingerprints.

But if you wipe your face after sweating and getting oily, like you do, there will be a lot more residual oil and inorganic salts.

Li Shu had considered that this situation might occur.

At the time of the incident, the suspect had been staying at the hotel for several days, looking for a suitable target.

In an underground hotel built in 81, the airtight and stuffy conditions made sweating quite normal.

He committed the crime at night, so he probably hadn't washed his face. It might also have been his first time committing a crime, and he was nervous.

So it's very possible that wiping sweat on your face will leave more oil residue on your hands.

Li Shu no longer hesitated and followed the procedure.

The sample was placed in, gold flakes were cut into the evaporation boat, and then the vacuum process began.

Reheat to evaporate.

After evaporating for a certain period of time, switch to zinc.

At this point, the timing is crucial. If it's too short, the zinc layer will be too thin, and the contrast won't be visible. If it's too long, the zinc layer will be too thick, and it will cover the lines.

This is also the main reason why Zhou Xuewen and his colleagues felt it was not easy to use; they didn't know how many times they would have to experiment to get the timing right.

Li Shu is fine; the system has the data and is very accurate.

After evaporation, cool and release the pressure.

If successful at this point, the hidden fingerprints should already be visible.

Li Shu took a deep breath and opened the door of the instrument.

Several fingerprints are clearly visible on the hanging galvanized sheet.

"Goodness."

Chen Shengkang let out a low shout and succeeded on his first try.

"Li Shu, you're really good at operating this thing."

When this thing was first sent to the institute, it was rarely used successfully. It failed every time it was used, so it's no wonder it was phased out.

Li Shu picked up the galvanized sheet, which was clearly visible.

"Director Zhou, what do you think? Can we give it a try?"

This method will work.

Zhou Xuewen took the galvanized sheet, looked at it, gritted his teeth, and nodded.

It's been 14 years, it's time to give it our all.