1995, Starting as a Criminal Investigation Expert

With such a major case occurring, leaving get off work is out of the question.

In the evening, my mom called me, and she called the police station directly.

She must have heard about Yanqiao's major case.

Even though I know Li Shu is just a technical police officer who works in an office, I can't help but worry.

Li Shu had already let her know he was safe over the phone, but she was still worried.

Sure enough, after returning from the case analysis meeting, Li Shu realized that his mother had been waiting for him for half an hour.

She actually made another special trip, only feeling at ease after seeing with her own eyes that Li Shu was alright.

Li Shu escorted her downstairs, and she kept muttering, "What time is it? Why aren't you off work yet? Aren't you supposed to be a technical police officer? You don't solve any cases."

"Technical police are still police."

Li Shu retorted, but seeing that she was still dawdling, he quickly helped her into the car.

A few years ago, after making some money, my dad got cocky and pestered my mom for half a year before finally getting a Santana.

My mom is very trendy; she drives even better than my dad.

After seeing his mother off, Li Shu went upstairs, where the meal had already begun.

My mom also bought some late-night snacks.

Peng Rong leaned against the window and must have seen it, teasingly saying, "Li Shu, I didn't realize your family was already doing so well."

Old Wei, who was standing next to him, joked that if someone was driving a Santana, then they weren't just aiming for a comfortable life, they were millionaires.

Li Shu blushed with embarrassment after being spoken to.

Zhao Yong waved his hand, telling everyone to stop teasing, hurry up and eat, and get back to work as soon as they were done.

Li Shu's task was to study that half of the fingerprint.

The first step is still filming.

The technical team has a dedicated darkroom.

I bought a rotating platform yesterday; it's the kind of rotating platform used for making Yixing teapots.

If it weren't for the sudden major case, we were already preparing to film today.

In the darkroom.

The rotating platform has been placed.

At first, I considered getting a mechanical one with high precision, but I couldn't get one right away, so I had to make do for now.

The solution is to place a large piece of paper under the table and draw a 360-degree scale on it with a ruler.

Use tape to attach a skewer to the rotating platform to act as a pointer, ensuring that it rotates one degree at a time.

Old Wei's real name is Wei Dejun. He is the leader of the team's camera crew, so naturally, he is in charge of filming.

The weapon was a Seagull DF-300 camera manufactured in Matsuura.

Paired with a macro lens.

The system has a complete method, but it is clear that this inventor was born in the future, and his final method of stitching together the negatives was done by computer.

Such methods no longer exist.

Li Shu initially envisioned using negatives to directly stitch them together.

After repeated discussions with Wei Dejun and others, it was determined that this method was not feasible.

The main difficulty lies in the operation.

Currently, 135 film is only 35 mm wide and 0.135 mm thick.

If you cut directly with scissors, cutting to a width of one millimeter, there is a high probability that burrs will remain on the edges.

When projected onto a magnifying machine, it will form uncertain feature points.

After all, the difference in fingerprint lines is only a fraction of a millimeter.

If they overlap, there will be a height difference, and even with a magnifying glass, there will still be a problem with inaccurate focusing.

The purpose of this method is to solve the problems of focus blur and bokeh during shooting.

In the end, it was Lao Wei and his team who came up with a solution.

Small negatives can't be directly stitched together, so we enlarge them and stitch them together.

Enlarge each negative, and when exposing the enlarged image, retain only the core one millimeter, the width where the image is most clearly in focus, and block out the rest of the area.

After the exposure is magnified, this area is cropped out and finally pieced together to form a complete fingerprint.

"Old Wei, is the lighting okay?"

Li Shu peeked out from behind the lightbox on the left side of the rotating platform and asked a question.

These lights were specially arranged.

The reason why curved fingerprints are not captured accurately is due to two main reasons, in addition to the deformation caused by pressure.

First of all, fingerprints are not flat; they have a certain degree of unevenness and are three-dimensional.

Residues left behind, such as sweat and oil, have a certain degree of reflectivity.

When it is on a curved surface, there will always be some points where the angle of incidence equals the angle of reflection, thus forming tiny light spots in the lens, resulting in blurred details in the shot.

Secondly, because it is a curved surface, there are differences in height.

When shooting with a macro lens, the depth of field is very shallow.

When focusing on the convex point of the curved surface, the left and right sides recede backward, resulting in out-of-focus images and unclear photos.

In the system's approach, side lighting was chosen to solve the first problem.

For example, if the light comes from the left, normally the fingerprint on the left side will be captured clearly, but the fingerprint on the right side will not be captured clearly because there is no light.

Normal photos wouldn't be taken like this.

But now, by shooting in segments, you can shoot only the center, the clearest position, thus completely eliminating the appearance of light spots.

After observing for a while, Wei Dejun gave Li Shu a thumbs up.

If it's feasible, then let's film it.

Li Shu and Wei Dejun worked together, taking one shot, then rotating the platform once, and then continuing to take shots.

Each photo needs to be checked to see if it's clear enough.

Because the support arm itself has a certain curvature, it cannot be completely perpendicular to the rotating platform.

This half of the fingerprint is roughly one centimeter wide.

Because the images are enlarged for stitching, and to ensure accuracy and find potential details, the plan is to retain a width of only 0.5 millimeters for each image.

In this way, at least 20 photos need to be taken.

To ensure accuracy and prevent any errors, we reshot the video.

A total of forty photos were taken.

Only now can we say that the first step is complete.

The next step involves using an enlarger, exposing and cropping the image, and then stitching it together.

Knowing the importance of this half fingerprint, Li Shu didn't feel tired while working. He even took the opportunity to practice on his own.

Then, to my surprise, I discovered that not only was my experience in fingerprint verification growing, but my photography skills were also improving.

That would kill two birds with one stone.

By dawn, through the efforts of several people, a complete photograph was pieced together.

Han Jianjun held up the photos he had taken and compared them with those taken previously.

"You know what, there are some subtle differences, especially on the left and right sides."

Han Jianjun compared them carefully.

Zhao Yong and his team had also stayed up all night, their eyes bloodshot. They took the photos and examined them carefully, nodding in agreement, and then beaming with joy, saying, "It seems that this method of rotating the camera is useful. It has solved the problem of extracting fingerprints from curved surfaces."

"Li Shu, wow, how did you even get such a brain?"

Zhao Yong looked astonished.

Everyone has a brain, so why is yours so special, able to come up with good solutions one after another?

Just then, Xu Qiang arrived.

He came over last night to ask about the progress of the fingerprinting.

"You're out?"

His eyes lit up, and he quickly stepped forward, took the photo, examined it carefully, and after a long while, frowned and said, "There's no difference."

Han Jianjun snatched it away, saying irritably, "If I could make you see the difference, then you should be the team leader."

Xu Qiang gave an awkward smile and turned to give Li Shu a thumbs up.

First it was the rapid positioning method, and now this curved surface shooting method. This year's recruitment has actually yielded an unexpected talent.

"Old Xu, have you caught the guy?" Han Jianjun asked.

Everyone else looked at Xu Qiang.

Another night has passed.

Xu Qiang said speechlessly, "You guys, why do you have to bring up something I don't want to talk about? Look at my face! If we had found the person, would I be this worried?"

Han Jianjun gave him a sympathetic look and reminded him, "You only have four days left out of the five-day deadline. You'd better step up your game."

One advantage of being a technical police officer is that you won't get scolded if the case isn't solved in the end.

"So we have to rely on you guys."

Xu Qiang clasped his hands together, bowed to the crowd, and said, "Grandpas and grandmas, please give me some clues!"

Li Shu remained silent.

Judging from Xu Qiang's reaction, it's clear how difficult the investigation is going to proceed.

"Captain Han, when will the system arrive?" Li Shu asked.

The fingerprints are ready; now all that's needed is the AFIS system for analysis and comparison.

"Soon."

Han Jianjun glanced at the clock on the wall and said, "They said the train leaves around 9 a.m., it's a 15-hour journey, and we'll arrive by dawn."

From now on, Nanjiang will also be a city with an AFIS fingerprint comparison system.