Chapter 25: Frantic Wiping

Wiped the cup, then the glass; wiped the glass, then the mirror; wiped the shiny surfaces, then the rough ones; wiped the rough ones, then the fine ones; wiped the fine ones, then the soft ones; wiped the soft ones, then the hard ones…

Investigative work, viewed broadly, appears varied and complex, but viewed closely, it’s all small, fragmented tasks.

Police say case resolution comes from resource accumulation—and this is evident during on-site investigation.

For example, with DNA and fingerprint collection, laypeople often assume that if a suspect left DNA or fingerprints at the scene, investigators will find them—but in reality, no advanced instrument exists that can accurately detect all fingerprints and DNA within a given range.

Take fingerprints: they’re first divided into three types—visible, plastic, and latent. The first two are visible to the naked eye; the third, as the name implies, requires specific methods to reveal. And those methods vary depending on the location and material of the fingerprint—powder, fuming, smoke, chemical reagents, different chemical reagents, different chemical reagents…

Therefore, for on-site investigators or trace evidence technicians to obtain a single fingerprint, they must first judge where fingerprints might exist, then observe—using the naked eye with light or angle, breathing on smooth surfaces to observe, or employing magnifiers or UV light. Only after confirming the fingerprint’s location do they proceed to dust for prints, or use iodine fuming, silver nitrate, or other chemical methods for extraction.

Thus, if a Spider-Man had crawled across the ceiling, the on-site investigators would most likely miss the fingerprints on it.

DNA is even more troublesome than fingerprints.

Fingerprints are at least visible; DNA is sometimes visible, sometimes purely a guess.

For instance, extracting DNA from the victim’s toothbrush—the officer doing the extraction naturally sees nothing, merely guessing that the toothbrush likely contains DNA.

For items with lower probability—like shirts, bed sheets, or even cups, porcelain bowls—the presence of DNA is pure speculation.

At this point, the difference in investigative skill becomes stark. Some investigators think from the suspect’s perspective, guessing his movements and actions to locate possible traces, then methodically dust for prints; others just bundle up shirts and bed sheets en masse, or randomly cut out a few pieces without caring whether they’re useful…

But overall, the more personnel involved, the higher their skill level, and the more time and effort invested, the greater the chance of discovering clues and evidence.

Jiang Yuan’s techniques, in Wang Zhong’s view, were extremely strong—but only suitable during a homicide case. If he applied the same approach to a theft case, it would be nearly impossible. The cost of one DNA test, just for reagents, is nearly a hundred yuan; the number of tests possible per unit time is severely limited, and you might wait so long that the biological samples grow mold before they’re processed…

“Let’s wipe the bathroom again.” Jiang Yuan finished processing the bedroom; the sky had turned dark.

Wang Zhong slapped his forehead, pointing at a large box of evidence bags: “Why not come back tomorrow? There are over a hundred of these—send them all to the lab, they’ll go insane.”

Jiang Yuan explained: “More than half of these probably won’t yield DNA, so no reagents will be used. The killer cleaned too thoroughly—look at the bedroom, many fingerprints were wiped clean. Plus, the victim bled heavily; the killer must have spent considerable time in the bathroom—washing rags, possibly even showering or laundering clothes. The bathroom has a high probability of yielding DNA.”

“Xiao Hu and the others thought the same, and they wiped everything carefully,” Wang Zhong said.

“They wiped too roughly,” Jiang Yuan said, recalling how Xiao Hu and the others had handled the body—now he had no reservations.

“Sigh… fine, I’ll stay late with you today.” Wang Zhong hadn’t noticed before, but now he realized the team’s on-site investigators were indeed sloppy—like his own fingerprint technique, the best praise they could get was “usable.”

In the past few hours, the overlooked fingerprints Jiang Yuan had found might not solve the case, but they’d already proven that he and Lao Yan’s “usable” standard was insufficient.

“Uh…” the old man by the door couldn’t sit still: “We need to go home for dinner.”

“Sign and leave,” Wang Zhong said—he never expected the elderly witness to stay long. Witnesses are always like this: either refuse to get involved, or wander around talking nonsense, or simply lack patience.

Wang Zhong had no intention of lecturing him—he simply brought over the on-site inspection record, flipped to the signature page, had the two men sign their names, then opened the door and let them out, warning: “What you saw and heard today, you may only disclose in court or when questioned by official authorities—never leak it otherwise, or you’ll face criminal liability.”

The two old men nodded impatiently, muttering, “Got it, got it.”

Wang Zhong nodded as if it were routine, closed the door, and returned to help Jiang Yuan wipe for DNA and fingerprints.

The bathroom lighting was poor, making wiping even harder.

But Jiang Yuan wiped with great enthusiasm.

The Crime Scene Investigation Level 4 skill didn’t just improve his operational ability—it also raised his cognitive level.

Various criminal theories all point to one truth: the longer a criminal stays at the scene and the more he does, the more mistakes he leaves behind.

The killer in this case appeared meticulous—cleaning the scene thoroughly, even calmly showering—but in Jiang Yuan’s view, this merely revealed his amateurism and arrogance.

Modern DNA technology can even identify identity from sweat. To clean a bathroom to absolute perfection in a short time is impossible. A slightly more professional criminal would at least have wrapped the entire bathroom in plastic, then taken and buried or burned the plastic—reducing leaked evidence dramatically.

But then, there’d be tape or adhesive residue at the scene…

Jiang Yuan wasn’t sure exactly where he’d find the killer’s DNA—he was young, energetic, and just wiped furiously.

Wipe.

Wipe, wipe…

Jiang Yuan was still in the novice excitement phase; this was the only crime scene he’d ever investigated since gaining the Crime Scene Investigation Level 4 skill. Naturally, he was fully experimenting and practicing.

In on-site investigation skills, technique is vital, and meticulousness is essential—but physical stamina, energy, and focus are what elevate you to the next level. Was Xue Huaiyi’s fall from Wu Zetian’s favor because his experience and technique improved, making him disliked? Obviously not. Similarly, the Zhang brothers weren’t discarded for being young, reckless, and impulsive.

Wang Zhong lacked all these qualities, but though tired, he was spurred on by Jiang Yuan and pushed himself to keep going.

Jiang Yuan paid special attention to wiping the bathroom ceiling and corners.

The longer he worked, the more meticulous and confident he became.

This house had no wet-dry separation, but the bathroom was small; water splashed onto walls and ceiling during showers was highly likely, and impossible to fully clean in a short time. The only question remained: could DNA be recovered? Blood traces were probably washed away or destroyed, but to wash away all DNA traces? This killer was still an amateur.

Ordinary people, committing unplanned murder, normally don’t study relevant skills in advance. Even if they do, they won’t study seriously or thoroughly—and thus, they’re highly likely to be caught by police who study seriously and master the craft.

Night fell.

Jiang Yuan and Wang Zhong dragged their heavy bags back to the police station, heading straight for the DNA lab.

Nowadays, cases solved directly by DNA are increasing, and police departments are investing more in DNA labs. Even the poor Ningtai County had, under various subsidies and policies, built a DNA lab according to ministry standards.

This lab was also a money pit: a three-person unit consuming over 10% of the police budget annually, with costs constantly rising.

But contrary to Wang Zhong’s expectations, the DNA lab quietly accepted the mountain of evidence bags without complaint.

They didn’t even carefully inspect or criticize the biological samples Jiang Yuan and Wang Zhong delivered.

“How did Old Qian from DNA become so easygoing?” Wang Zhong muttered as he followed Jiang Yuan into the forensic office.

In the forensic office, Wu Jun hadn’t gone home either. Like most detectives, he sat at his desk organizing today’s paperwork. He stood up, rubbed his eyes, and said slowly: “This afternoon, the team leader blew up. The problem now is no leads—the DNA lab is desperate for you to submit samples, so they won’t be idle.”

Jiang Yuan laughed: “Not working at night counts as idle?”

“The team leader hasn’t gone home either,” Wu Jun said. “If they don’t find anything soon, they’ll go back and re-examine the scene themselves.”

Wang Zhong looked at Jiang Yuan and clicked his tongue: “They’d just waste their time. With their on-site skills? I’m not exaggerating—fine for ordinary cases…”

Wu Jun cut him off: “Do you think they don’t know that themselves?”

“Uh…” Wang Zhong had no reply, and silently returned to his office.

Jiang Yuan, however, was thoroughly satisfied. He tidied up and spread out his military cot right in the office.

Until the commotion woke up the officers who’d been up all night.

“DNA matched someone—Captain Liu took a team out,” Wang Zhong burst into the office first, still with sleep crust in his eyes.