1995, Starting as a Criminal Investigation Expert

Not only Wei Dejun, but also Han Jianjun, immediately frowned.

Zhao Yong noticed the change in Wei Dejun's expression and hurriedly said, "Old Wei, that matter wasn't your fault."

The elderly members of the team nodded in agreement.

Li Shu glanced at Peng Rong subconsciously, wanting to ask what was going on.

Then he remembered that Peng Rong hadn't arrived at the team yet when the incident occurred.

This case is from 90, so five years have passed.

The incident occurred in New Taipei District, which didn't even exist at that time.

The deceased, Li Haiping, was the owner of a materials trading company in Luoshe Town. He died in his own warehouse.

Wei Dejun said, "That's what I say, but over the years, I've occasionally thought, if I had just carried an extra scale with me back then, this case might have been solved."

At this point, he looked up at Li Shu, his tone earnest: "Li Shu, I've been doing this for over ten years and have made mistakes, but none have had such serious consequences as this one. If you can match that fingerprint, I... I really have to thank you properly."

He even stepped forward to bow.

Startled, Li Shu quickly got up and stopped him.

Han Jianjun said in a deep voice, "Old Wei, the matter is over, and the bureau has already reached a conclusion. It's not your fault. But you're right, Li Shu, there are still some clues in this case. Think of a way to see if you can find a match and get rid of this worry for Old Wei."

If a mistake had been made back then, but the case had been solved, then it would have been fine.

The key case remains unsolved, and although five years have passed, it has become a major worry for Wei Dejun.

Li Shu nodded quickly and said, "Captain Han, I haven't looked at the case file in detail."

This is no small case; the case file filled several boxes.

"I only saw that a blurry, inaccurate fingerprint was extracted from the explosive device at the scene, and it didn't match. I don't know the specifics. What exactly happened?"

Wei Dejun mentioned the scale, and the case file also said it was inaccurate. Could it be that the scale was not included?

Wei Dejun, who has worked for many years, wouldn't make such a basic mistake.

Han Jianjun waved his hand, telling those who had things to do to go ahead and get to work, then sat down and said, "Well, the situation was rather special at the time."

After the case was reported, the city's criminal investigation team dispatched officers immediately.

The on-site investigation was led by Han Jianjun.

"We could smell a very strong gasoline odor even before we got to the site."

Han Jianjun's thoughts drifted back to 90.

Li Haiping runs a trading company that deals in office paper all over the country. He has a storefront in the town where he runs his company.

At the same time, he rented a large courtyard in a village near Luoshe Railway Station and built a warehouse there.

They usually live in the warehouse.

The incident occurred around 10 p.m., and some neighbors had already heard the commotion and chose to call the police.

Wang Benyi was the first to arrive at the scene and found Li Haiping bound, stabbed in the abdomen, and unconscious.

They were rushed to the hospital.

He suffered massive bleeding and died halfway there.

The suspect not only tied up and stabbed Li Haiping, but also poured gasoline all over the warehouse in an attempt to set it on fire.

"Gasoline is one thing, just be careful, but the real problem is that they also found explosives."

He gave a brief description of the situation at the scene.

Because the warehouse was relatively enclosed and contained only paper, Li Haiping would issue invoices and keep accounts in a small cubicle.

There was a safe, and more than 13 yuan of cash was stolen.

Li Haiping was tied to a stool behind his desk, and under the desk was a shoebox. It was only during the on-site investigation after he was taken away that they discovered homemade explosives inside the shoebox.

Clearly, the suspect's aim was to stab Li Haiping, then plant explosives to kill him, while simultaneously setting fire to the warehouse outside.

"That guy made a time-delay device to give himself time to leave the scene, or maybe to torture Li Haiping. But the technology was rather crude. When we opened it, it had already been activated, but it didn't explode."

Recalling these past events, Han Jianjun couldn't help but feel lingering fear.

Li Shu could imagine how terrified everyone would be when they discovered the bomb.

Han Jianjun continued, "That's where the problem lies. When we found the shoebox, we suspected it didn't belong to the victim. We wondered if there would be fingerprints on it, so we sprayed it with Ningxi Telin, and sure enough, there were."

Ningxitelin is ninhydrin, which is commonly used in the extraction of sweat fingerprints.

Logically speaking, finding fingerprints should be a good thing.

But the problem is the bomb.

After spraying the medicine and revealing fingerprints, Zhao Yong called to Wei Dejun beside him to prepare to take a picture, while instinctively opening the cardboard box to see what was inside.

Upon closer inspection, they were shocked to discover explosives inside with a countdown timer set to zero.

Everyone present was stunned.

Han Jianjun quickly ordered everyone to evacuate the scene.

Under these circumstances, Wei Dejun hurriedly took a few photos of the fingerprints on the surface of the shoebox and quickly left the scene.

They then contacted bomb disposal experts, but it was more than half an hour later when they arrived at the scene and defused the bomb.

Then came the fatal blow.

In the midst of the chaos, Wei Dejun didn't have time to set up the scale.

After everyone evacuated, the door to the small room was left open, and gasoline evaporating outside the warehouse seeped into the room, contaminating the fingerprint.

At this point, Li Shu finally understood.

Gasoline, as a very strong organic solvent, will dissolve substances such as oleic acid and fatty acids in the sweat fingerprints when it evaporates in a closed warehouse.

This results in blurred or smudged fingerprints, making it impossible to take a second photo.

"Old Wei, this isn't your fault at all. If you hadn't snapped those photos, there wouldn't be any fingerprints," Li said.

This isn't making a mistake; it's actually doing a great service.

In that situation, who knew when the bomb would explode? Who would dare stay put, set up the scale, and take careful photos?

Wei Dejun waved his hand and said bitterly, "How should I put it? At the time, I thought this case would be easy to solve. The neighbors all saw the suspect, and there was explosives left at the scene. It was obvious that he had a grudge against the victim."

"Who knew that after investigating for more than two months, we still couldn't find the person. So I thought, what if we find this person through fingerprints? Wouldn't it be because of me that the case hasn't been solved?"

Han Jianjun raised his hand to tell him to stop talking.

Five years have passed, so there's no point in discussing it anymore.

"Li Shu, do you have a solution for fingerprints without a scale?"

This is plain noodles, and the tissue box is made of kraft paper.

The suspect carried it with him and left multiple fingerprints on it.

But because of this, some fingerprints overlap, and some are rubbed off.

After developing the photos, only one whorl-shaped fingerprint was clearly identifiable.

The central area is intact, but it's unclear which finger it is.

Most importantly, there is no scale.

At that time, there was no AFIS system. Even with the human eye, it was difficult to confirm identity because the density and shape of fingerprint lines vary from person to person. Without a scale, and given that it is a common whorl pattern, it was very difficult to confirm identity.

Therefore, when teaching fingerprinting at school, Zhang Lu emphasized the importance of the scale more than once.

"Yes, I have."

Li Shu immediately replied.

Yes, there is. The system has information on this.

After all, everyone makes mistakes. The system has a journal article that describes a similar situation.

"No, you really have it?" Peng Rong exclaimed, his eyes wide.

You have everything I ask you for, you're like a magic lamp.

Wei Dejun's eyes lit up, and he asked first, "What method?"

Li Shudao said, "Captain Han, since we're missing a scale, why don't we just find one ourselves?"

Han Jianjun was still in shock.

I just asked casually, and it turns out there's a solution.

The key point is that your tone is too casual. What do you mean by "just find one yourself"? That's useless. How can you find one?

"What do you mean?" Han Jianjun pressed.

Li Shudao said, "You should know that, apart from exceptional cases, a person's fingerprint has about 20 to 30 lines per centimeter. We can use this as a basis to repeatedly adjust and put it into the system for comparison."

"The specific operation method is somewhat similar to the surface unfolding system. For example, if you select 20 lines and set them to 1 centimeter, you can artificially specify a scale."

"If it's not good enough, then keep expanding, select 21, and then up to 30. This micron-level difference can basically achieve the 1:1 ratio required by the system."

In this journal article, the authors refer to this method as the line-to-number ratio method.

Some things are like window paper; they're transparent at a glance.

Han Jianjun almost instantly understood the principle behind it. He gasped and looked at Li Shu with a look that went beyond shock; it was fear.

This kid is terrifying; he can come up with a brilliant idea so easily.