Attending ex-girlfriend's wedding, arresting the groom's officer on the spot

Zheng Kaibin's bank statements showed that his personal finances were sound, with no major debt disputes or unusual financial transactions. His call records showed no suspicious calls other than those with his sister Zheng Kailan, colleagues Zhao Wei and Li Mengmeng, and clients. His travel history indicated that in the week leading up to the incident, Zheng Kaibin did not go to any unusual places or leave the city, except for his normal commute to and from get off work and his routine between his company and home.

The investigation team focused their efforts on the unfamiliar man mentioned by the neighbors. By reviewing the CCTV footage from the entrance of the complex (the internal surveillance system was outdated, with only the entrance having cameras), they indeed found footage of Zheng Kaibin talking to an unfamiliar man at the entrance around 10:20 PM on November 3rd. In the footage, the unfamiliar man was wearing a black coat, a black hat, and a mask, completely obscuring his face, making it impossible to see his features. The two talked for about ten minutes, after which the unfamiliar man turned and left, walking towards the north side of the complex, while Zheng Kaibin entered the complex.

The team retrieved surveillance footage from the area following the direction the stranger had left, but due to the low coverage of the surveillance system, the stranger disappeared after reaching an intersection without surveillance cameras. Based on the stranger's height and build in the surveillance footage, the team interviewed nearby residents and shop owners, but found no one who recognized him.

The investigation has once again reached a stalemate. Although the deceased's identity has been confirmed, a comprehensive investigation into his interpersonal relationships has failed to uncover a clear suspect. The stranger who argued with Zheng Kaibin at the entrance of the residential complex, while highly suspicious, cannot be further investigated due to the inability to confirm his identity.

Wang Shuai convened another meeting with his team to review the leads, re-examining all the information they had gathered. "Currently, Zheng Kaibin's social relationships seem relatively simple, with no obvious grudges or financial disputes. The stranger is the only suspicious point, but we can't confirm his identity or his relationship with Zheng Kaibin," Wang Shuai said. "Have we overlooked something? For example, Zheng Kaibin's private life—is it possible he has secrets or hidden connections?"

Zhang Kai added, "Our forensic department re-examined the physical evidence collected at the scene. The fingerprints on the dagger were indeed those of the deceased, Zheng Kaibin, and no other fingerprints were found. Further analysis of the fiber samples revealed that, apart from the fibers from the deceased's clothing, the gray and black fibers collected at the scene did not match the fiber samples we collected from Zheng Kaibin's home and company. These were likely left by the suspect. However, no one has been identified as being related to these fibers so far."

Yang Lin said, "Let's review Zheng Kaibin's call records and social media information again to see if we've missed any clues. Also, we haven't checked Zheng Kaibin's vehicle information yet. Does he own a car? Where was his vehicle on the day of the incident?"

An investigation revealed that Zheng Kaibin owned a black Volkswagen sedan with license plate number 京A·XXXXXX. The team immediately retrieved the vehicle's driving trajectory and discovered that on the day of the incident, the car was parked in the underground parking lot of the Sunshine Garden residential complex, remaining there from the evening of November 5th until after the incident. The team conducted a thorough examination of the vehicle; the interior was clean, and no suspicious traces or items were found.

Subsequently, the team members investigated Zheng Kaibin's social media accounts and found that he had very few friends, mostly colleagues and clients, and the chat history was all work-related, with no unusual chat information found. However, the team members discovered that Zheng Kaibin had an anonymous social media account with very few friends, and most of the chat history was deleted, leaving only a few chat records with a user with the screen name "Lone Ranger." The content was rather cryptic, mentioning words such as "transaction," "confidentiality," and "location," but without specifying what kind of transaction it was, or the location and time of the transaction.

“This ‘lone wolf’ is very suspicious!” Wang Shuai said. “We must find out the real identity of this ‘lone wolf’ as soon as possible.” The technical department immediately began to track the anonymous social media account and the “lone wolf” account, but because both accounts were encrypted and used virtual IP addresses, the tracking work was very difficult.

As time passed, the investigation stalled once again. The investigators didn't let their guard down, continuing their investigation around the clues of the stranger and the lone wolf, but without any breakthroughs. After confirming her brother's identity, Zheng Kailan remained emotionally unstable, repeatedly calling to inquire about the case's progress, putting immense pressure on Wang Shuai and his team.

Twenty days after the incident, Zhang Kai suddenly approached Wang Shuai with a new forensic report. "Captain Wang," he said, "we conducted a more thorough examination of the dagger recovered from the scene. We found a small amount of skin tissue fragments in the crevices of the dagger's handle. Previously, the amount was too small to detect. We performed DNA typing on these fragments, and the results show that the skin tissue does not belong to Zheng Kaibin; it was likely left by the suspect!"

This discovery thrilled Wang Shuai: "Great! This is the most direct lead on the suspect so far! Immediately enter this DNA data into the national DNA database for comparison, and at the same time compare it with the DNA of all the people we have investigated!"

The technical department immediately began DNA comparison. However, after two days, no match was found. The suspect's DNA was not recorded in the national DNA database, nor did it match the DNA of Zheng Kaibin's relatives, friends, colleagues, business partners, and other individuals previously investigated.

Although no matching DNA information was found, this discovery gave the investigators renewed hope. "At least we now have the suspect's DNA information. As long as we investigate suspicious individuals later, we can directly confirm whether they are the suspect through DNA comparison," Wang Shuai encouraged the team. "We will continue to expand the scope of the investigation, focusing on clues about the stranger and the 'lone wolf,' while also conducting a comprehensive investigation of the floating population and individuals with criminal records around the unfinished building in the northern suburbs, extracting their DNA information for comparison."

In the days that followed, the investigation team once again threw themselves into the intensive investigation. They conducted a comprehensive search of densely populated areas around the unfinished buildings in the northern suburbs, including urban villages, construction site dormitories, and gathering places for homeless people, collecting DNA samples from nearly a hundred suspicious individuals for comparison, but none of them matched the suspect's DNA. (End of Chapter)