1995, Starting as a Criminal Investigation Expert

Joking aside, Han Jianjun couldn't ignore Li Shu's efforts in devising a rapid positioning method.

"Li Shu, please continue."

The case analysis meeting was held, but the complete fingerprints did not match.

The suspect was clearly a seasoned veteran, leaving no useful evidence at the scene.

On the other side, in addition to visiting migrant workers, the team even began to investigate the sales of angle grinders on the market.

This is enough to illustrate the predicament of the case.

We're almost at a dead end, so we're starting to grasp at the minuscule clues.

Han Jianjun had actually considered that half fingerprint.

After all, these are fingerprints, left by the suspect. They are the most direct and conclusive physical evidence that can pinpoint the target.

Unfortunately, the fingerprints were in poor condition, and there was nothing he could do.

Li Shu looked around, grabbed a ballpoint pen from the desk next to him, pressed his thumb against it at an angle, and showed it to everyone.

"Look, the middle is concave, the flesh is squeezed together, and the lines are dense, so it looks like the fingerprint of an index finger."

The thumb is large, and the lines are wider.

But now that they're all squeezed together, it's easy for people to make misjudgments.

"Then, the other person was holding the trophy, so they had to use their thumb to lift it up, which is why there are still some friction marks on the fingerprints left behind."

Scratches and fingerprints are the hardest to identify; they're essentially blurred.

"Most importantly, when we take photos to extract fingerprints, we take the photos directly facing the fingerprints."

Li Shu picked up his pen and gestured with his hand.

When you shoot a cylinder from the front, the curved surface will cause significant distortion on both sides.

"There's also the issue of lighting. When light shines directly on a cylinder, the lines on the sides may not be as clear due to light reflection."

When the light shines on it, the front is clear.

However, due to the angle and light reflection from the side, some details may be disturbed and affected.

After all, fingerprint ridges are at the micrometer level.

Han Jianjun unconsciously crossed his arms, lost in thought.

The others also showed thoughtful expressions.

Zhao Yong nodded and said, "Li Shu, just tell me your plan."

The situation Li described is actually what they encounter in their actual work.

For example, with a club-shaped murder weapon, the fingerprints left by the suspect are actually on this curved surface.

When extracting fingerprints from photos, there will inevitably be a certain percentage of distortion.

One solution is to use transparent paper to trace over the surface.

This can, to some extent, avoid proportional distortion.

But hand-tracing is difficult, let alone dealing with incomplete or stained fingerprints; encountering such a situation almost means giving up.

Li Shu picked up a book and then placed a water glass on top of it.

"It's like making Zisha teapots at Donglin; you need a rotating platform to shape them. So my idea is simple: to shoot while rotating."

Li Shu picked up another pen holder and placed it opposite him.

"This is the camera, which is fixed in place. The book is the rotating platform, and the water cup is our trophy. It takes a picture every time it rotates one degree from left to right."

"By taking dozens of photos at a constant speed and then overlaying the negatives, matching details to details, we should be able to reconstruct a fingerprint with more accurate proportions."

The system provides an introduction.

This fingerprint expert uses this method to take a picture, and then uses a computer and an algorithm to reconstruct the complete fingerprint.

Li Shu couldn't understand computer science, but he could refer to its principles.

It involves piecing together consecutive frontal photos to create a fingerprint image with realistic proportions, thus solving the problem of extracting fingerprints from curved surfaces.

Of course, this only solves the problem of the external proportion distortion. The problem of the concave compression in the middle still needs to be addressed by other methods.

But this is something that comes step by step.

In solving cases, we follow each clue one by one until we finally find the culprit.

Fingerprint comparison here, as long as it matches, can identify the suspect and directly solve the case, so it's normal to proceed step by step.

Guo Xiangyang stepped forward first, half-squatting down, and gestured back and forth with a water cup and a pen holder.

The crowd gathered around, silently pondering.

"That's interesting."

Guo Xiangyang muttered something to himself, then said, "If we shoot it like this, I feel it can solve the problem of distorted proportions on both sides."

He turned to look at Li Shu, and couldn't help but be surprised.

Just like a locator.

It looks like a simple change, but no one has thought of it or overlooked it.

And Li Shu was able to think of that.

This is enough to demonstrate that Li Shu has a keen intuition for solving problems.

That's what's truly precious.

Talent!

Guo Xiangyang silently made a judgment in his mind.

At this point, someone asked, "Taking and extracting the image is only the first step. The key is how to compare it next. Even if the proportions are correct, it's still incomplete and can't be compared."

The others nodded in agreement.

The most important question is how to compare them.

Everyone turned to look at Li Shu.

Li Shu was thinking about how to explain the principle of the partition comparison method and did not answer immediately.

To the general public, that meant there was no answer.

"Old Wei, you're putting people in a difficult position."

Peng Rong spoke up, still defending Li Shu, saying, "It's already remarkable that Li Shu was able to figure out a way to solve the problem of extracting fingerprints from photos. Incomplete fingerprints, that's a huge deal."

Several people nodded in agreement.

The comparison of incomplete fingerprints has always been a major challenge in criminal investigations.

If Li Shu can solve this problem, that would be incredible.

Old Wei smiled wryly and said, "Peng Rong, I didn't mean anything by it, I was just asking."

Zhao Yong waved his hand to signal people to be quiet, and then said, "I think it's already very good that Li Shu thought of taking photos like this."

"Think about it, incomplete fingerprints are troublesome, but what about complete fingerprints? We've encountered many situations where we need to extract fingerprints from curved surfaces. With this method, wouldn't the extracted fingerprints be more accurate?"

Everyone was taken aback before realizing this.

Han Jianjun nodded in agreement, saying that this, like the locator, was a method.

It doesn't solve a single, complex problem, but rather it can solve all similar problems.

That would be of immense value.

Looking at Li Shu again, Han Jianjun couldn't help but be surprised.

This kid is exaggerating a bit. He's only been here a few days and he's already come up with two solutions.

Unexpectedly, Li Shu nodded and said, "I do have a method that might work."

Everyone was startled.

Peng Rong's eyes widened. "We were just saying it casually, but you really have a way with things!"

Li Shu didn't care what others were thinking; he only had one thought in his mind: to solve the case.

He then said, "Captain Han, when I was in school, my teacher explained to us the principle of the AFIS system for comparing fingerprints."

Li Shu then picked out the important points and explained the comparison process of the AFIS system.

It's likely that many people on the team only know about the system but don't fully understand how it works.

"In summary, the process is as I described: first, collect the fingerprints, preprocess them, generate codes, store them, and when comparing them, compare the codes and, based on the overlap probability, give the fingerprint with the highest probability in the fingerprint database."

With the knowledge gained from the system, Li Shu has gained a deep understanding of the AFIS system.

Everyone was stunned.

Just as Li Shu thought, many of them only knew about this thing, but didn't know exactly how it worked.

Otherwise, this system wouldn't be so expensive, and the manufacturer wouldn't have to send people over.

It's about teaching you how to use it.

The total cost includes training fees.

Han Jianjun nodded blankly. He had been eyeing this system for two years and had been studying it, but he felt that he didn't know the specific working principle as well as Li Shu had explained.

He couldn't help but wonder, is the school teaching this comprehensive?

Tan Guoxiong, sitting in the corner, shared the same thought.

My head is full of questions.

Li said it was taught at school, but I've never learned that.