Blankly putting down the enamel mug in his hand, Old Bai looked bewildered: "I went to watch a Beijing opera yesterday afternoon and completely forgot about it..."

Liu Guodong: "..."

Liu Guodong didn't say anything, but there was a bit of resentment in his eyes.

Have we been slacking off this much?

Lu Chuan blinked in confusion and asked: "…Master, what's up?"

Two minutes later, a letter was placed in front of Lu Chuan.

"It was sent over by the Economic Investigation Team, asking us to help identify fingerprints, but the requirement is not to damage the envelope."

"Why didn't they send it to the Technical Identification Center?"

Because the Criminal Investigation side has its own crime scene investigation and trace inspection equipment, we've been able to handle technical identifications ourselves over the past few years.

But it's different for the Economic Investigation side. They don't have the personnel or equipment for this.

Evidence found during investigations needs to be sent to the Technical Identification Center according to procedure.

It shouldn't be sent to the Criminal Investigation.

"It was sent, but the quality of the Technical Identification Center at the Municipal Bureau… Extracting fingerprints from paper is already very difficult, let alone from a coarse fiber kraft paper envelope."

Liu Guodong had already put on gloves and was examining the envelope against the sunlight: "They couldn't do it over there, so the Economic Investigation people came to us."

Lu Chuan nodded, though given his understanding of Liu Guodong, Old Bai, and Yang Sen's capability, extracting fingerprints from paper without damage…

"Master, extracting fingerprints from paper without damage… must be difficult."

Liu Guodong snorted, putting down the envelope: "It's more than just difficult, fingerprint extraction from paper is not a small problem."

Extracting fingerprints is easiest on smooth, non-absorbent dry surfaces.

For instance, fingerprints on surfaces like phone screens and car door handles are least difficult to extract.

The completeness of the extraction is also higher, which means less time spent in subsequent fingerprint comparisons and a higher success rate in matching.

But extracting fingerprints from some rough and absorbent surfaces is extremely difficult.

Materials such as wood and fur are such examples.

Paper is the most representative among them.

Because paper is made of plant fibers, these fibers aren't visible to the naked eye, but they have large gaps and very poor smoothness.

The sweat and grease from fingerprints left on paper get absorbed quickly.

Generally, fingerprints on paper can be extracted using the ordinary iodine fuming method.

The principle of this method is that the sodium crystals in the fingerprint sweat react chemically with iodine fumes.

Thereby developing the fingerprint.

However, this method has a drawback: it damages the fingerprint.

That is to say, the chemical substances left in the fingerprint can only undergo one chemical reaction.

Afterward, the fingerprint will disappear, leaving a trace on the paper.

The difficulty of this task lies in the fact that the Economic Investigation side requires no traces left, so fingerprints must be extracted without damage.

Therefore, neither the iodine fuming nor the ice examination methods would work.

"Old Liu, those guys at the Technical Identification Center who don't do anything are asking the Economic Investigation to find us because they can't do it themselves."

Bai Wenhai was obviously a bit emotional: "Maybe we should just respond that it's not possible."

Liu Guodong looked at the envelope, arms crossed, deep in thought.

To be honest, if it were any other time, he would refuse without thinking.

But it's different now because Lu Chuan is in the Crime Scene Investigation office.

Lu Chuan showed great skill in collecting burnt and water-soaked fingerprints during the arson case and submerged corpse case in the South Suburb.

This indicates that Lu Chuan's abilities in fingerprint collection probably far exceed those of the three of them.

The question is, will there be any trouble following this help?

Or, is there any advantage?

Moments later, Liu Guodong turned to Lu Chuan: "Lu, do you have any solution?"

Lu Chuan didn't hesitate: "There is a solution, but we don't have the necessary equipment, and using ordinary methods to extract fingerprints without damage is practically impossible."

Liu Guodong's eyes lit up upon hearing this.

"What method?"

Old Bai also leaned in to listen to Lu Chuan speak: "A variable frequency laser spectroscopic analyzer."

Hmm?

"What's that thing?"

Old Bai clearly hadn't heard of it before.

"In recent years, using lasers for biological sample collection has been popular, but they all use fixed-wavelength lasers."

Liu Guodong and Old Bai nodded; they had heard of it but never seen it.

It's known that this kind of laser collection equipment is effective at detecting human teeth, bones, blood, sweat, seminal stains, saliva, etc.

However, this equipment is too expensive, and the Haizhou City Criminal Investigation Team doesn't own it.

"But for fingerprints on paper, this fixed-wavelength laser equipment cannot develop fingerprints on paper."

"Adjusting the wavelengths is required."

Lu Chuan didn't mention the specific frequency adjustments needed because, without the equipment, explaining it would be pointless.

"Besides this method, is there any other way?"

Lu Chuan shook his head: "Certainly not, other methods would damage the fingerprint and leave traces, only this method I mentioned."

"And the equipment… how much does it cost?"

When asking this question, Old Liu's eyes were filled with anticipation.

Everyone knows that the Economic Investigation Team is loaded with money.

Let's not mention other things, just look at the cars they have.

They have the entire BBA* series, even high-end models.

As for the Criminal Investigation Team?

Just two vehicles, one of them even being ten years old.

The reason the Economic Investigation side wants to extract fingerprints without damage this time is because the envelope has a special mark.

Acquired through special means, damage or traces on the evidence would prevent sending the envelope back.

The suspect might discover that the envelope was tampered with.

So…

This is a chance to exploit... no, to strengthen the friendship between Criminal Investigation and Economic Investigation.

"Over four hundred thousand or so, and it has quite a wide range of applications. There's one available for sale right in Haizhou City."

Lu Chuan originally didn't know the exact price but used one in the Tianzhou City Criminal Investigation Team a few days ago.

He asked Li Kai about this equipment's details.

"Over four hundred thousand..."

No big deal.

Liu Guodong packed the letter and left the office immediately: "Lu, wait for me in the office!"

Three hours later, just as it was about to be lunchtime.

Liu Guodong returned hurriedly.

Along with him came a variable frequency laser spectroscopic analyzer.

"Master… this is?"

Lu Chuan didn't expect that after one round outside, Liu Guodong truly brought back the equipment.

"Haha, it's a sponsorship from the Economic Investigation side. Although it isn't our asset, as long as we help them with fingerprint analysis, this equipment is for our team's free use!"

Tsk, tsk.

Old Bai circled around the equipment, clicking his tongue: "The Economic Investigation sure has money, over four hundred thousand, approved so quickly!"

Liu Guodong agreed with Old Bai: "They've encountered a major case, and this envelope is the key."

"Alright," Liu Guodong turned to Lu Chuan: "The equipment and the envelope are in your hands."

"Looking forward to your good news!"

"No problem!"

*Note: BBA refers to high-end car brands like BMW, Benz, and Audi.

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