Diary of a Criminal Investigator

The case of Song Tiejun has come to a temporary conclusion.

The subsequent investigation process was directly handed over to the Tianzhou City Public Security Bureau by the major crime unit.

Of course, whether Song Tiejun really only killed five people is something nobody can say for sure.

No one can definitively say if the Wang Family River is the only place where Song Tiejun disposed of bodies.

After all, even with the five bodies that were found, from a Crime Scene Investigation perspective, there are no direct traces of Song Tiejun on them.

However, according to domestic law, a conviction doesn’t require direct evidence; logical reasoning is still admissible.

If the suspect cannot prove their innocence to a certain extent, it can only be concluded that they committed the murder.

Of course, there is direct evidence too, such as the bloodstains on the wall of Song Tiejun’s house, the saws and axes used to dismember bodies, and the furnace used to burn the heads.

These all confirm that Song Tiejun indeed committed murder.

However, given the current forensic technology, it’s impossible to determine exactly who the victims are.

"Teacher Lu, our last case here really relied on your hard work."

Wang Chuanmin, the captain of Tianzhou City Criminal Investigation Team, hasn’t been idle these past few days. They’ve been solving another murder case.

This is also why Wang Chuanmin reported the case to the provincial bureau immediately after it was filed; they truly couldn’t handle it all.

Moreover, given the complexity of the case, Wang Chuanmin wasn’t entirely confident about solving it, so reporting it to the provincial bureau was the only option.

Although the case is now solved, there was a certain element of luck involved in the process.

If Sun Jianguo and Zhang Erhe hadn’t gone to Old Street, or if they went there and didn’t drink lamb soup at Song Tiejun’s house...

Or if they drank the soup but didn’t talk about past incidents with Song Tiejun...

Then Song Tiejun might really have gotten away with it.

At that point, if no new clues appeared, solving the case would have been as hard as climbing to the heavens.

Lu Chuan had visited Tianzhou City several times and was fairly familiar with the captain there, Wang Chuanmin.

"Captain Wang, you’re too kind. The last case was really just a coincidence, I didn’t help much."

Participation in the Tianzhou City skeleton case was a significant battle that made Lu Chuan’s name known.

It was through this case that Lu Chuan came to the attention of the provincial bureau, leading to many subsequent participations in major cases at the provincial level.

"Teacher Lu, now that things are wrapping up here, when do you plan to return?"

"I’ll arrange a car to take you back."

"Tomorrow. The major crime unit doesn’t have much left to do, so I plan to return to Haizhou City tomorrow."

"No need for a car, I’ll take the train back; it’s quite fast."

The distance between Haizhou City and Tianzhou City is not far, there’s no need to fly, and taking the train is just right.

"Oh, how can that be? If Old Qin finds out, he’ll blame me for not being a good host."

"There’s been a murder case recently, I’ve been extremely busy. Otherwise, I’d definitely invite Teacher Lu for a good drink!"

Listening to the tone, Lu Chuan was no longer the naïve rookie he was over a year ago.

"Captain Wang, if there’s anything in your current case I can help with, please don’t hesitate to let me know. When I came, Captain Qin specifically instructed me that the Tianzhou City Criminal Investigation Team and the Haizhou City Criminal Investigation Team are neighbors and have close cooperation, and that I should learn from you."

"Haha!"

Wang Chuanmin laughed heartily. Who wouldn’t like someone like Lu Chuan?

Competent, not arrogant, and pleasant to talk to.

"Teacher Lu, with your assurance, I’m relieved. To be honest, the current case is quite tricky. If you have time, could you lend a hand?"

"Time isn’t an issue, but Captain Wang, you know I’m specialized in Crime Scene Investigation; beyond that, I might not be much help."

"And please, just call me Lu. I’m not worthy of being called Teacher Lu."

"Haha, alright then, I won’t stand on ceremony. It is indeed a matter of Crime Scene Investigation, involving fingerprint clues."

In solving a case, there’s no room for formalities. Lu Chuan followed Wang Chuanmin directly to his office.

"Here are the case files, Lu, take a look first."

The case files weren’t thick, only six pages.

The case itself wasn’t particularly complicated.

A week ago, the North Suburb Police Station in Tianzhou City received a report; a murder had taken place at the North Suburb logistics warehouse.

A security guard, patrolling the logistics base, discovered a body in an abandoned warehouse.

"The crime scene was clean and tidy. The perpetrator even used a broom to clean up footprints, leaving no trace."

"Moreover, the suspect left the murder weapon inside the victim’s body, and we extracted some clues from the weapon’s handle."

The photos in the case file show a boning knife, with faint fingerprint-like marks on the handle.

"Lu, do you think you could conduct an analysis on these marks?"

Wang Chuanmin was a bit embarrassed.

Fingerprint identification requires actual fingerprints to be effective.

However... anyone, even a layman, would know that the stuff on the knife handle is not related to fingerprints at all.

The day after the crime, Wang Chuanmin actually approached his connections in the provincial bureau, and their fingerprint expert had already looked at it, with a three-word response.

What a joke.

Lu Chuan frowned, this thing...

"Captain Wang, is it convenient to take a look at the weapon?"

With this level of "fingerprint," you couldn’t deduce anything just from photos.

"No problem, the weapon is in the evidence room, I’ll have someone bring it over now."

Ten minutes later.

The weapon was already in Lu Chuan’s hands.

After a careful look, Lu Chuan had his evaluation.

The blurry marks on the knife handle were indeed left by fingerprints, but they weren’t direct fingerprint marks.

Clearly, the perpetrator was very cautious, not only thoroughly cleaning footprints as they left the scene but also disguising their fingerprints while committing the act.

The perpetrator obviously had a lot of confidence in their disguise, so even though some blurry marks were left on the knife handle, they didn’t bother to clean them further.

"Captain Wang, this identification and analysis... is quite difficult."

"Moreover, the method the suspect used... is not as simple as wearing gloves."

Oh?

Wang Chuanmin only had a basic understanding of fingerprint analysis, not an in-depth one.

Lu Chuan continued to explain: "Most perpetrators, when committing a crime, wear gloves to avoid leaving fingerprints."

"Cotton gloves effectively prevent fingerprint traces, but they’re thicker, with poor friction, making it challenging to control the strength used during the crime."

"Some perpetrators use surgical latex gloves, but these are very thin and might imprint the perpetrator’s fingerprints onto the weapon indistinctly."

"Additionally, fingerprints can be recovered from the inside of such latex gloves."

"Besides wearing gloves, there are many other ways to make fingerprints disappear."

"For instance, applying glue over the fingerprints can conceal fingerprint information, or soaking fingerprints in high-concentration sodium hydroxide can erase them. Soaking in dilute nitric acid can cause the skin to peel, making fingerprints disappear temporarily."

"Apart from these methods, burning with a cigarette, mechanically rubbing the fingerprints, etc., can make fingerprints disappear temporarily."