1995, Starting as a Criminal Investigation Expert

Inside the laboratory where the team's physics and chemistry group conducts routine inspections.

Han Jianjun and others surrounded Li Shu.

Outside the door, Xu Qiang, Xiao Rui, and the others waited anxiously.

The main force is still outside, of course.

Because of previous cases, the branch has, to some extent, developed a path dependence on Li Shu's fingerprint identification.

But it's impossible for them to do absolutely nothing, just like Tang Weidong said.

The investigation into the case is ongoing.

Firstly, by conducting extensive interviews at the crime scene, it was discovered that the suspect, having no means of transportation after committing the murder, would have had to leave on foot, and might have been witnessed by someone.

Secondly, we tried to reconstruct Liu Yanjuan's whereabouts that night.

When the body was discovered, the car was running and the meter was still on. By looking at the mileage, we could determine how far the car had traveled, thus reconstructing the distance from the pick-up point to the crime scene.

However, it was late at night, and the distance was nearly ten kilometers, making it difficult for this work to make progress in a short period of time.

Therefore, Xu Qiang knew very well that if Li Shu could extract the suspect's fingerprints, it would be faster than any other method.

Li Shu took a measuring cup and poured in 100 milliliters of anhydrous ethanol.

"TMB is displayed in blue-green."

While preparing the solution, Li Shu also explained why he had to do it this way.

"Tetrabromofluorescein, like ammonia black, has a strong affinity for proteins in the blood and is then excited by light sources of a specific wavelength."

"Look at you."

"1 gram of alcohol-soluble eosin is mixed with 100 ml of anhydrous ethanol, and then 2 to 3 ml of glacial acetic acid is added to balance the pH value."

This staining agent is called EOS solution.

Li Shu strictly followed the system's recipe for preparation.

"It's very simple, and you don't need to heat it up or anything. Just mix it according to this ratio."

The group exchanged glances.

It is simple.

But what's not simple is, how do you know that eosin Y can react with proteins? It's an industrial dye, and nobody used it for bloodstain testing before.

Also, why does it only excite under specific wavelength light sources?

How did you know about this specific frequency band?

If you don't understand, just ask.

Peng Rong subconsciously raised his hand, wanting to ask a question.

Zhao Yong stopped him with a look: Don't ask, just listen carefully.

Li Shu quickly prepared the solution and poured it into the spray bottle.

Tan Guoxiong handed over a car door handle from the side.

It's not physical evidence from the scene; it's from a disassembled car of the same model.

Out of caution, we should still conduct an experiment.

Apply the coating to a large area and allow it to air dry naturally.

Once dry, prepare a simple weak acid solution using glacial acetic acid. After your hands are dry, rinse them with the weak acid solution to remove excess dye.

"You can wash it with confidence, the dye from the reaction has already adhered to the protein."

Let it air dry.

"Walk."

Li Shu led the group straight to the dark room.

Wei Dejun's side is ready.

This dye only exhibits orange-red fluorescence at a specific wavelength of 450nm.

The team used a 365nm long-wave ultraviolet lamp to investigate the site, which was unable to excite the light.

On the way back, Li Shu prepared two methods.

One method is hand-rolling.

Use a regular full-band xenon lamp, paired with a bandpass interference filter.

Li Shu didn't know if Nanjiang had any filters, so he simply asked Zhou Xuewen, who readily agreed to help him find one.

Matsuura has many companies and laboratories, so we found one easily.

Li Shu brought it with him when he changed trains in Songpu.

By using a filter and a xenon lamp, a simple handcrafted alternative can be made.

But since it's hand-rubbed, the effect might not be as good.

Therefore, there are alternative solutions.

That means taking the physical evidence and heading straight to 803.

They are truly wealthy and have the connections to access the most advanced technologies and equipment.

Zhou Xuewen said that their institute has a multi-band field general-purpose survey light source.

Its official name is the On-Site Trace Evidence Discovery Instrument. It was researched and invented by the Second Research Institute of the Ministry and passed the Ministry's appraisal in May of last year.

It hasn't been widely promoted yet, but Matsuura already has it.

This device can emit light in multiple wavelengths as needed.

If the presentation here isn't good, then I'll have to go to 803 and ask for their help.

Inside the darkroom, nothing could be seen on the black doorknob.

Under Wei Dejun's control, the blue light source focused, and in just a moment, a glowing fingerprint appeared on the handle.

Orange-red, extremely conspicuous in the dark.

It's not clear enough; the diffuse reflection of light makes it look somewhat blurry.

But this is the second step in addressing the problem.

This step is merely to prove that the staining method is feasible.

"That's really something, Li Shu."

Han Jianjun leaned closer and said something with a double meaning.

Everyone crowded around to see the effect.

Zhao Yong sighed, "That's pretty good sensitivity."

The latent blood fingerprints on the test subject were left after repeatedly wiping with paper after touching blood and after being mixed with sweat on the face.

Very little blood remained.

As he spoke, he leaned closer, squinted to examine it carefully, and then said, "And I don't feel dizzy at all; the effect is very stable."

TMB has extremely high sensitivity; it can detect blood diluted 100,000 times, comparable to luminol.

Li Shu nodded and said, "That's right, this EOS staining agent has good sensitivity. Also, it's a protein staining agent, just like amino black."

"Therefore, it has the same properties as amino black, which is that it is more effective against old fingerprints with deactivated enzymes."

TMB is an enzyme-catalyzed reaction that is highly effective against fresh blood fingerprints.

However, if too much time passes, the enzymes in the blood become inactive, and the effect of TMB will decrease significantly.

At this point, staining agents that focus on protein reactions are actually more effective.

Therefore, it can handle some old blood fingerprints.

Ammonia black is a commonly used method in China now.

Like TMB, Ammonia Black appears bluish-black and cannot be used on dark substrates.

So ultimately, EOS is a specific method used for special situations.

"Good heavens, so according to that logic, Li Shu, you've invented a protein dye, haven't you?" Cao Junfei exclaimed in realization.

This is an invention.

Han Jianjun was stunned for a moment, then realized what he meant and nodded repeatedly: "That's right, this is an invention. You guys, don't go around telling everyone."

He hurriedly reminded everyone.

Everyone nodded blankly.

Peng Rong's eyes darted around, and he hurriedly said, "Captain Han, if we're talking about inventions, can't we apply for a patent and then sell it for money? Wow, Li Shu, you're rich! You even have a patent!"

In Peng Rong's mind, invention is patent, and patent is money.

The group exchanged glances and nodded in agreement.

Newspapers often report on who invented a patent and made a lot of money from it.

When the topic of money came up, Li Shu quickly said, "Brother Rong, don't try to scam me."

Peng Rong said, "How am I cheating you, Li Shu? I'm just reminding you. Don't worry, no one will take it from you. Just remember, when you make a lot of money, treat me to a meal at Jufengyuan."

Behind the light source, Wei Dejun nodded in agreement.

I'm not envious, but I can at least treat myself to a meal.

Forget it.

Li Shu shook his head again, saying, "Brother Rong, you really dare to dream, and with such a large sum of money. Think about it, besides us, who else has this need? And who am I supposed to sell it to?"

Only the police, and fingerprints used under specific conditions, will be used.

Moreover, the dosage is extremely low.

I just casually prepared 100 ml, enough to last until it expires.

"And another thing, if I apply for a patent for this, then who will manufacture it? My dad? And then my dad will sell it to our bureau. Don't you think you're trying to screw me over?"

I'm a police officer and a member of the Communist Party, how can I go into business and make money?

Secondly, the cost of this thing is outrageously low, so how much can I sell it for?

So from beginning to end, Li Shu never thought about making money from this.

Now, after being reminded by Peng Rong, and after thinking about it, Li Shu felt that the best option was still to write it as a thesis.

Then, it's most worthwhile to apply for personal technological inventions through the bureau and get the bonuses and honors.