Chapter 46: The Wealthy Economic Crime Investigator

Blankly setting down his enamel mug, Old Bai looked completely bewildered. "I went to see Peking Opera yesterday afternoon and completely forgot about that matter..."

Liu Guodong: "..."

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

*Has our slacking off reached this level already?*

Lu Chuan blinked and asked in confusion, "...Master, what's the matter?"

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

"It was sent over by the Economic Investigation Detachment. They're asking for our help to identify fingerprints, but they require that the envelope not be damaged."

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

The Criminal Investigation side had its own forensic scene investigation and fingerprint detection equipment, so they could handle technical identifications themselves in recent years.

However, the Economic Investigation side was different; they lacked both the talent and the equipment in this area.

According to protocol, evidence discovered during a case must be sent to the Technical Identification Center. It shouldn't be sent to Criminal Investigation.

"It has already been sent, but given the level of the Municipal Bureau's Technical Identification Center, extracting fingerprints from paper is difficult enough, let alone from a coarse-fiber kraft paper envelope."

Liu Guodong had already put on gloves and was holding the envelope up to the light to examine it. "They couldn't do it, so the people from Economic Investigation came begging us."

Lu Chuan nodded, but based on his understanding of the capabilities of Liu Guodong, Old Bai, and Yang Sen, non-destructive fingerprint extraction from paper...

"Master, non-destructive fingerprint extraction from paper... that must be difficult, right?"

Liu Guodong snorted and set the envelope down. "It's more than just difficult; fingerprint extraction from paper is a significant challenge in itself."

The easiest fingerprints to extract are from dry surfaces that are smooth and non-absorbent. For example, fingerprints on carriers like mobile phone screens or car door handles are the easiest to extract. Furthermore, the integrity of the extraction is higher, meaning less time is spent on later fingerprint comparisons and the probability of a successful match is greater.

However, extracting fingerprints from surfaces that are rough and absorbent is extremely difficult. Carriers like wood or fur are prime examples.

Paper is the most representative of these. Because paper is composed of plant fibers—which are invisible to the naked eye but actually contain large gaps between them—its flatness is extremely poor. The sweat and oils left by a fingerprint on paper are quickly absorbed.

Generally, fingerprint extraction on paper can be completed using the standard iodine fuming method. The principle of this method is that the sweat in a fingerprint contains sodium crystals, which undergo a chemical reaction after iodine fuming, thereby developing the fingerprint.

But this method has a drawback: it destroys the fingerprint. That is to say, the chemical residues of the fingerprint can only undergo a chemical reaction once. After that, the fingerprint disappears, and marks are left on the paper.

The difficulty of this task lay in the fact that the Economic Investigation side required that no marks be left behind; they wanted non-destructive extraction. Therefore, neither iodine fuming nor the cyanoacrylate (superglue) method would work.

"Old Liu, those useless people at the Technical Identification Center... if they can't do it themselves, they just have the Economic Investigation side come to us."

Bai Wenhai was clearly emotional. "We might as well just reply saying we can't do it."

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

To be honest, under normal circumstances, he wouldn't have even thought twice before refusing. But things were different now; the Forensic Scene Investigation office had Lu Chuan.

In the South Suburb Arson Case and the Reservoir Corpse Case, Lu Chuan had shown great skill in collecting burnt fingerprints and water-submerged fingerprints. This indicated that Lu Chuan's strength in fingerprint collection likely far exceeded that of the three of them.

The question was, after helping this time, would there be any subsequent trouble? Or rather, would there be any benefits?

After a moment, Liu Guodong looked at Lu Chuan. "Xiao Lu, do you have a way?"

Lu Chuan did not hesitate. "I do have a way, but we don't have the relevant equipment. Using ordinary methods, it's basically impossible to extract fingerprints non-destructively."

Liu Guodong's eyes lit up upon hearing this. "What kind of way?"

Old Bai also leaned in to listen to Lu Chuan. "A variable-frequency laser spectroscopy analyzer."

Huh?

"What on earth is that?" Old Bai had clearly never heard of it.

"The laser-based biological sample collection popular in recent years uses fixed-wavelength lasers."

Liu Guodong and Old Bai nodded; they had heard of such things but had never seen them. They had heard that these laser biological sampling instruments have excellent detection effects on human teeth, bones, blood, sweat, semen, saliva, and more. However, these things are too expensive, and the Haizhou City Criminal Investigation Detachment certainly didn't have one.

"But for fingerprints on paper, a fixed-wavelength laser biological sampling instrument cannot develop the fingerprint on the paper. You need to adjust the wavelength band."

Lu Chuan didn't specify exactly what frequency needed to be adjusted; regardless, without the instrument, saying it was useless.

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

Lu Chuan shook his head. "Definitely not. Any other method would destroy the fingerprint and leave marks. This is the only method I know."

"That instrument... how much does it cost?"

When asking this question, Old Liu's eyes were practically glowing.

Who didn't know that the Economic Investigation Detachment was rolling in money? Setting aside everything else, just look at the cars they are equipped with. They have a full set of BBA (BMW, Benz, Audi), and even high-end models.

And the Criminal Investigation Detachment? They only have two Land Cruisers, one of which is ten years old.

The reason the Economic Investigation side required non-destructive extraction this time was that this envelope had special markings. It had been obtained through special means specifically to collect fingerprint evidence; if it were damaged or if marks were left, the envelope could not be sent back. The suspect would then realize the envelope had been tampered with.

So... this was a great opportunity to squeeze them... no, to deepen the friendship between Criminal Investigation and Economic Investigation.

"About four hundred thousand yuan. This thing has quite a wide range of uses, and it's available for sale right here in Haizhou City."

Lu Chuan didn't actually know the exact price, but he had used one at the Tianzhou City Criminal Investigation Detachment the day before yesterday and had asked Li Kai about the equipment.

"Four hundred thousand..."

Not a big problem.

Liu Guodong packed the letter and left the office directly. "Xiao Lu, wait for me in the office!"

Three hours later, just as they were about to finish work for lunch.

Liu Guodong rushed back, looking winded. At the same time, he brought back a variable-frequency laser spectroscopy analyzer.

"Master... this is?"

Lu Chuan hadn't expected that Liu Guodong would actually go out and bring the thing back.

"Haha, it's sponsored by the Economic Investigation side! Although it's not our asset, since we are helping them with fingerprint analysis, this thing is on free loan to our detachment!"

Tsk tsk.

Old Bai circled the instrument half a turn, clicking his tongue. "The Economic Investigation side really is loaded. Four hundred thousand, and they got it approved so quickly!"

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

"Alright," Liu Guodong looked at Lu Chuan. "I'm leaving the instrument and the envelope to you. I'll wait for your good news!"

"No problem!"