Diary of a Criminal Investigator-Chapter 339: Target Range

Locard’s Law of Exchange has been validated at every crime scene, without exception.

This arson case is a prime example.

After committing the murder, the culprit set a big fire at the scene, destroying all traces inside the room.

However, some traces outside the room still remained.

A partial footprint may be the key evidence to identify the suspect.

Returning to the team, Lu Chuan went straight to the crime scene investigation laboratory.

The first task was to identify the vehicle tire tracks.

From the preliminary analysis at the scene, the tire tracks found outside were the same as those found inside in terms of pattern and wear level, but differed in ground contact area.

This indicates that the electric vehicle left traces outside while carrying a load.

Now, Lu Chuan’s task is to calculate the load of the electric vehicle based on the difference in tire ground contact area.

This is quite challenging.

Many factors can influence the tire contact area, such as tire wear, air pressure, or the hardness of the ground.

Fortunately, the tire tracks Lu Chuan found were on hard ground, with minimal difference.

On the other hand, if the electric vehicle’s tires were intact, the changes in air pressure inside the tires indoors and outdoors wouldn’t be very significant.

This way, Lu Chuan could calculate the load of the electric vehicle more accurately.

And this load should be the weight of the killer.

Moreover, a partial footprint was found next to the tire tracks.

Based on the outline analysis, Lu Chuan was confident he could estimate the full length of the footprint, which would allow for calculating the height range of the owner.

Though it sounds easy, executing it poses many challenges.

Lu Chuan’s skills in tire track identification and footprint identification analysis are at a beginner level, with limited methods mastered.

After more than three hours of work, it wasn’t until after 7 PM that Lu Chuan’s task was initially completed.

He dialed Liu Guodong’s number and roughly reported the findings.

"Alright, bring the report over directly. I’m in Captain Qin’s office; you can report directly to Captain Qin."

Ten minutes later.

"Based on the tire tracks from the scene, we can roughly determine the suspect’s weight to be around 150 kilograms, with a height between 1.7 to 1.8 meters."

This time, Lu Chuan’s estimate of height had a larger margin of error, given there was only a partial footprint.

Qin Yong, holding Lu Chuan’s report, was in a good mood!

"150 kilograms?"

"Plus a height of less than 1.8 meters, that’s quite a distinctive feature."

Lu Chuan was also pleased, as the suspect’s physical features were quite distinctive.

kilograms meant the person was likely obese.

This measurement reinforced the assumption that the person who left the partial footprint outside was the suspect.

Because the two deceased inside, although partially carbonized, appeared to be lean.

Even if both sat on the electric vehicle, they wouldn’t weigh 150 kilograms.

Of course, if they were carrying something, that would be a different story.

So, Lu Chuan reported this as a strong possibility.

For Qin Yong, however, this strong possibility was a key tool for solving the case.

"Old Liu, send Lu Chuan’s report to Ren Qiang and Sun Jun. They’re checking the victims’ connections to see if anyone matches these physical traits."

"Yes!"

People shouldn’t stand out too much.

A normal build is fine; if too obese or too thin, it leaves a stronger impression.

This strong impression isn’t necessarily bad, but if such a person commits a crime, the chances of being recognized increase significantly.

Liu Guodong sent Lu Chuan’s report to the group, and within less than ten minutes, there was feedback. 𝙛𝒓𝒆𝙚𝒘𝒆𝓫𝙣𝓸𝙫𝓮𝒍.𝒄𝒐𝓶

It was from Zhang Meng, who was taking statements from the victims’ parents.

Zheng Caixia’s parents provided an important lead.

"Before Caixia married Zhao Ming, she went on several blind dates. There was someone named Zhang Jianzhong who nearly married her back then. I’ve met him—he’s quite fat."

Zhang Jianzhong!

"Where is Zhang Jianzhong?"

"Our people are already investigating. Soon..."

Before Ren Qiang finished his report in Qin Yong’s office, the phone rang.

"Brother Qiang, we’ve found the person!"

Unexpectedly, Zhang Jianzhong lived in a self-built house on Shanghe Street.

Zhang Meng and others had even visited his home for investigation this morning.

"This guy lives just two alleys away from the victims. This morning, when we sent officers for a door-to-door inquiry, he even mentioned participating in firefighting."

In front of a residential house, over a dozen police officers were ready.

It’s now 8:20 PM.

Ren Qiang glanced at the lights inside: "Are we sure he’s inside?"

"Yes, Zhang Jianzhong works at a nearby food factory and gets off work at six every day. Neighbors saw him enter the courtyard."

Ren Qiang nodded: "Ensure safety and make the arrest!"

With the order given, over a dozen people broke through the gate and rushed in.

"Are you Zhang Jianzhong?"

When Ren Qiang entered the courtyard, Zhang Jianzhong was already pinned to the ground by five people and had been handcuffed.

This guy was indeed very fat and surprisingly strong.

Even with five able-bodied men holding him down, he could still struggle a bit.

"Do you know why you’re being arrested?"

"Heh, heh, how did you... how did you find me?"

Half an hour later.

In the Criminal Investigation Team’s interrogation room.

Zhang Jianzhong wasn’t placed in the interrogation chair. Weighing over 200 pounds, he was too large for it.

Zhang Meng and his team brought in an ordinary stainless steel chair, handcuffed and shackled him, providing some restraint.

"Zhang Jianzhong, tell us why you killed Zhao Ming and Zheng Caixia?"

"Heh, heh, there must be a reason for killing them, but how did you know it was me?"

"I set such a big fire; any fingerprints or footprints must have been burnt away."

"Burnt away?"

After Zhang Jianzhong was brought in, Lu Chuan didn’t even need to collect the footprint; a glance told him that the partial footprint at the scene was his.

With this evidence, even if Zhang Jianzhong said nothing, a conviction could be secured without a confession.

"You killed someone and even rode away on their electric vehicle. How greedy of you."

Zhang Meng and Zhang Hui were in charge of the interrogation.

"That electric vehicle was bought by me, so of course, I took it!"

"Your electric vehicle?"

Zhang Hui was a bit surprised: "What’s your connection with Zhao Ming and Zheng Caixia’s vehicle? Did you know them?"

"Of course there’s a connection. Before they married, I knew Zheng Caixia. She agreed to marry me two years ago, and I bought that electric vehicle for her."

"I also lent her 50,000 yuan, but back then, there was no IOU. Two years passed, and she married someone else without returning my money."

"Do you think such a woman deserves to be killed?"