Diary of a Criminal Investigator

The crime scene is a self-built house, with a room area of not large, probably only about 40 square meters.

At 127 Songjiang Road, there are about ten self-built buildings, which have not been demolished, and many tenants live here.

When the police received the report, the victim’s information had been basically confirmed. The deceased was a tenant here.

"Captain Qin, the person renting the house is named Zhang Xiaotian, the young man among the four victims. The other three, the young woman is Zhang Xiaotian’s sister, and the other two are Zhang Xiaotian’s parents."

The landlord is currently outside being questioned by Zhang Hui.

"When did Zhang Xiaotian start renting here?"

"Last March."

The landlord is a middle-aged man, who discovered the victim’s death and was the one who called the police.

"I rented my house to him for 800 yuan a month, with an agreement of one-month deposit and three-month advance payment. He hasn’t paid the rent this quarter, so I came over to check today, but unexpectedly, when I opened the door, I found several people all dead."

The landlord’s face is now pale, and his speech is somewhat unclear, clearly terrified.

"Does Zhang Xiaotian usually live here alone or with his family?"

"Alone, but not at first. Last year, he lived here with another man for a while, then that man seemed to have moved out. Since this year after the New Year, Zhang Xiaotian has been living here alone."

"Do his parents often come over?"

"Once or twice, usually on weekends. His parents also work in Haizhou City. The whole family works here, but I don’t know the specific situation very well. I heard about it in a chat with his father."

"Do you have any information about the man who lived with Zhang Xiaotian last year?"

"Yes, yes, yes, when they lived here, they needed to register their ID cards according to the current rental requirements. I have copies of their ID cards."

"It’s upstairs, I’ll get it for you now."

Outside, other members of the crime squad are also questioning other tenants in the building.

"I didn’t hear any noise last night. I was too tired from work and slept pretty heavily when I got back."

"His parents came yesterday afternoon, I’ve seen them before. They usually stay here for a night, but it seemed like there was no noise last night."

"Our surveillance here doesn’t work, it’s all broken. The landlord won’t pay for repairs, even though we’ve talked to him about it many times."

"Zhang Xiaotian seems to work as a mechanic at a car 4S shop, but we aren’t particularly clear on the details. He usually comes back late and isn’t really sociable with us."

"I think it was the man who lived with him last year who did it. You don’t know, the two of them were in a homosexual relationship."

"When the man moved out last year, he almost got into a fight with Zhang Xiaotian. Things were crashing inside, and I could hear it from next door."

Most of the information from the investigation isn’t very useful.

In real life, everyone lives their own lives, and not many people have the time to worry about others, so most people can’t provide any valuable clues.

However, Zhang Xiaotian’s neighbor knew slightly more information.

According to the information provided, Zhang Xiaotian was very likely a homosexual, and the man who lived here with him last year was his partner.

A few minutes later, Zhang Hui obtained a copy of the ID card of the man who lived with Zhang Xiaotian last year.

Wang Junshan.

"Check where this person is now."

While the investigation continued outside, Lu Chuan’s crime scene investigation also proceeded.

Because the floor of the entire room was basically covered with a layer of fresh blood, Lu Chuan and Old Yang laid down some crime scene investigation boards when they came in to minimize damage to the scene.

Normally, when blood leaves the body, it can coagulate within 3 to 15 minutes.

If the amount of bleeding is large, the accumulation and spraying can extend the coagulation time slightly, but it will not exceed 30 minutes.

Blood coagulation is a natural clotting function of the blood itself.

Generally, when the body suffers accidental injury resulting in bleeding, blood will coagulate in a short time.

There is a substance in the blood called thrombin, which is normally inactive.

But when the blood flow accelerates or the permeability of the blood vessels increases, this thrombin substance is activated, forming thrombin, which then generates fibrin.

This fibrin forms a lattice-like substance outside damaged blood vessels, which is too small for platelets to pass through, so platelets clog the grid, forming a clot that prevents further bleeding.

Normally, everyone has this coagulation function, but a small number of people are born with coagulation disorders, causing slow blood coagulation after injury, requiring special hemostatic methods.

However, the body’s own coagulation function has a certain range.

The human vascular system includes arteries and veins. Many arteries are deeper beneath the skin, while the blood vessels that can be seen with the naked eye on the surface are mostly veins.

The coagulation function mostly works for venous injuries. Generally, if an artery is damaged, the coagulation function cannot successfully stop the bleeding.

After the death of four people at the scene, blood coagulated differently from normal coagulation. Not all blood thrombin in the body was activated during massive spraying.

Instead, it was activated consecutively during the spraying process, so some blood coagulated quickly while some took longer.

Of course, the scene blood Lu Chuan and others see now has basically all coagulated. The time since the victim’s death should be around 5 to 6 hours.

Among the four people on the bed, two died from their carotid arteries being severed by a sharp weapon, causing massive bleeding leading to death.

The other two were stabbed in other areas, resulting in death.

The victims with severed carotid arteries are two males, one middle-aged and one young.

The two female victims on the ground, the young woman was stabbed in the abdomen resulting in death, and the middle-aged woman was stabbed in the chest.

"There are signs of a struggle."

Yang Sen pointed to the two female victims on the ground.

The two males died instantly, with virtually no signs of resistance, but both females had scratches and blood on their bodies and hands, indicating a clear struggle.

Lu Chuan nodded: "The bloodstains by the bed have been wiped, suggesting that the killer might have been injured during the struggle and could have left blood behind."

Liu Guodong, standing on a crime scene investigation board, moved to the wiped bloodstains and observed: "It seems they just used water to rinse it?"

"Didn’t use any detergent?"

"Probably not. I’ll take a sample, and we can go for analysis later. If the killer truly bled, we can match the DNA information."