National Forensic Doctor

Chapter 1306: Chapter 1232: Hanging by a Thread

Within the forensic building of the Beijing Bureau, there’s its own Physical and Chemical Laboratory, considered a rather luxurious setup, because even Ningtai County Bureau’s building number 9 doesn’t have one.

Jiang Yuan found a clean lab bench and had Mu Zhiyang and Wen Ming help him carefully clean it with alcohol before pulling out the two plastic ropes and observing them meticulously.

These were currently the most valuable clues found, apart from the body. Although they found these two plastic ropes early in the garbage-sifting process, an experienced police officer must realize that clues aren’t linearly distributed.

Making full use of every clue you know about is the most basic respect for criminal investigation. Whether you receive a lot of clues and evidence at once or find a tiny bit by sheer luck, utilizing them as best as you can is the only thing a police officer can do and should do.

"Length 131 centimeters. Width 3 centimeters."

"Length 246 centimeters, Width 3 centimeters."

Jiang Yuan patted the two plastic ropes repeatedly to ensure no further details were available in terms of shape and then carefully untied the ropes, measuring the length and width first and then observing along the plastic rope bit by bit.

The so-called plastic rope is actually a wide and flat plastic band.

Its thickness is extremely thin, making the rope semi-transparent. The width is 3 centimeters, roughly equivalent to slightly more than two male fingers, but less than three, not counting those with larger hands.

In practice, people habitually twist the plastic rope to use it in its rolled-up form.

In other words, the plastic rope is used by scrunching it along its width.

This way, the creases created in the folded plastic rope could trap minute evidence.

Thus, Jiang Yuan took special care to clean the experiment table again while keeping a camera filming the tabletop continuously. He then carefully unfolded the plastic rope and sampled it segment by segment.

The plastic rope had been buried in the garbage pile for an unknown number of days, with some areas clearly soaked by the leachate from the pile. This high-concentration organic wastewater is devastating to organic evidence; whether it’s DNA or anything else, once in contact with this leachate, it goes to waste.

However, since both ropes were folded and compressed under other garbage, some creases formed relatively sealed environments.

Theoretically, if there is evidence, it might exist in these spots.

Jiang Yuan examined from the untied end all the way to the knotted section, meticulously inspecting each segment with a magnifying glass before sampling.

This spot is where evidence is most likely to be found.

Previously, Jiang Yuan, upon reaching this stage, would leave the rest to the technicians in the Physical and Chemical Laboratory.

Nowadays, equipped with Level 5 physical and chemical analysis skills, Jiang Yuan naturally took the task upon himself.

However, any level of technician is faced with multiple-choice questions at this point.

It’s said that modern technology has advanced significantly, capable of testing and analyzing even minute quantities of substances.

Yet, when sampling, there’s always an amount involved, and critically, no machine can precisely and accurately process the sampled evidence. Some treatments are damaging or even minimally damaging, meaning that after one type of test, conducting others becomes impossible.

Given this, the practice usually involves conducting non-destructive tests first, followed by minimally destructive and destructive tests in the laboratory.

To avoid garbage leachate contaminating the sample, Jiang Yuan first collected the sample. Reaching this step, he also had Mu Zhiyang pull the curtains and begin with non-destructive projects.

He first used a multi-band light source to scan, switching between 365nm ultraviolet, 450nm blue light, 535nm green light, and 850nm infrared, to check for fluorescence reactions.

Of these, ultraviolet can detect blood, various bodily fluids, and residues of certain narcotic plants like hashish. Blue light can find fingerprints, glue, and some synthetic fibers. For example, 502 adhesive glows with white fluorescence, while polyester shines blue. Green light can detect drug residues, with cocaine producing yellow-green fluorescence, while chemical burns may show bright spots. Infrared could reveal certain inks and paints and might also detect charred substances.

In summary, if someone bought a handheld multi-band light source, every time their partner returned home, drawing the curtains and scanning might expose whether they were smoking marijuana, engaging in SM activities, or using cocaine while being fully painted.

The two plastic strips before him were clean.

Of course, this doesn’t prove their innocence, merely that the first wave of macroscopic inspection yielded no results.

Jiang Yuan then opened the curtains, had people photograph the entire length with a high-resolution camera, and then, under a stereomicroscope, picked visible particles from within the folds using micromanipulators, storing them separately in sample tubes. This step qualified as minimally destructive.

The final steps were PCR and elemental analysis, namely the well-known DNA testing and component analysis.

Having completed the entire process, night had already fallen outside.

Wen Ming emitted a light snoring sound.

Mu Zhiyang, curled up in a corner, played on his phone, bored.

The technician in the Physical and Chemical Laboratory had no choice but to accompany Jiang Yuan, lest he damage the expensive SEM and GC-MS equipment.

"Let’s wait for the results." Jiang Yuan stood up, patted Wen Ming, and said, "Let’s go back."

"Ah, did we solve the case?" Wen Ming jumped up abruptly, still a bit dazed.

Jiang Yuan shook his head and then turned to Mu Zhiyang, asking, "How’s it going on Director Liu’s side?"

"They’re still investigating. We’ve found a few similar plastic strips in the market, but there seem to be no major differences between them. We need to identify the manufacturers before we can trace the distributors and buyers." Mu Zhiyang paused, then added his own conclusion, "It doesn’t seem easy to track down."

"Okay, let’s get some rest and discuss it tomorrow," Jiang Yuan didn’t say much more. Various physical and chemical tests needed time to run. Only once in the car did he review the day’s technical analyses but wasn’t in a hurry to draw a conclusion.

The next day.

Jiang Yuan arrived at the forensic building early.

The Cold Case Squad and Cui Qishan’s Fourth Group had also moved headquarters there, setting up a meeting in the forensic building’s conference room to hold a discussion.

Various reports from the Physical and Chemical Laboratory had also been delivered.

After a night of overtime, the laboratory technicians eventually managed to prepare most of the reports Jiang Yuan needed.

Jiang Yuan examined them one by one, and others passed them around to review as well.

At this point, one sample’s conclusion caught Jiang Yuan’s attention.

"Acrylamide and benzoic acid." Jiang Yuan lightly shook the report and asked, "What contains these substances?"

"The most common places to find benzoic acid are in food, medicine, paints, plasticizers, and other industrial fields," recited Wang Chuanxing, being well-read.

"How about acrylamide?" Liu Jinghui inquired further.

"In cosmetics and chemical raw materials as well as in certain foods, if I recall correctly, it’s carcinogenic," Wang Chuanxing began checking his pad.

Jiang Yuan said, "Maillard reaction. All high-temperature fried foods contain acrylamide, including fried steaks, fried dough sticks, fried chicken, and tempura, among others."

"Is the murderer a chef?" Liu Jinghui instantly reacted, adding, "Normal cooking shouldn’t include benzoic acid, right? Benzoic acid is in prepackaged food?"

"Various sauces contain it too," Wang Chuanxing replied after checking his information. "In terms of food, it’s found in soy sauce, juices, various flavorings, all of which are carcinogenic."

"When are we going to arrest such people?" Liu Jinghui took a deep breath, frowning, "So even regular cooking might expose someone?" noveldrama

Jiang Yuan shook his head, "The residue on the plastic strip indicates a large amount, not just slight exposure... The victim rode a bicycle to Jin Mountain. List all the nearby businesses — how many of them sell food?"

"Not many," Wang Chuanxing immediately located the list. These had been compiled days prior.

Quickly, he pulled out a list of businesses along the route, then extracted the food vendors from it.

"A fried chicken shop, a meat sandwich place, pancake stalls, fast-food restaurants, convenience stores..." Liu Jinghui counted, finding there were only a few dozen shops, so he stated, "Let’s question each one, ensuring to take statements from both the chefs and the store owners!"