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

"In addition, Yang Lin and Yang Sen, you two work with the technical department to re-examine the physical evidence collected at the scene to see if any details have been missed. Everyone, keep up the good work. The more difficult the situation, the more we must persevere and find a breakthrough as soon as possible."

After the meeting, Zhang Kai immediately returned to the forensic identification center and arranged for Xiao Lin to conduct further examinations on the deceased's samples. "Xiao Lin, first, enter the deceased's DNA sample into the national DNA database for comparison, focusing on investigating the relatives of recently missing persons and individuals with criminal records. In addition, conduct dental tissue examinations on the deceased's teeth to analyze their dietary habits and regional characteristics; perform isotope analysis on the bone samples to determine the deceased's place of origin."

Xiao Lin immediately followed Zhang Kai's instructions and began working. After entering the deceased's DNA data into the database, the system began automatic comparison. However, the comparison process lasted all day, and no matching information was found until evening. "Teacher Zhang, the results of the national DNA database comparison are in. No DNA information matching the deceased was found, neither for missing persons nor relatives of criminals," Xiao Lin reported somewhat dejectedly.

Zhang Kai frowned: "Continuing with isotope testing of the dental tissue and bone might narrow down the scope of the investigation." He then personally operated the equipment to examine the deceased's dental samples. "The enamel thickness of the deceased's teeth was normal, the dentin development was good, and no regional dental characteristics such as fluorosis were found, indicating that the deceased may have lived in a non-high-fluoride area for a long time. The wear on the tooth surface was relatively light. Considering the age, it is speculated that the deceased's diet consisted mainly of refined foods, and they may have engaged in mental or light physical labor, rather than heavy physical labor."

Bone isotope testing takes longer. Preliminary results show that the carbon and nitrogen isotope ratios in the deceased's bones are consistent with those of urban residents, while the oxygen isotope ratios point to the local area or surrounding regions, ruling out the possibility of a distant migrant. "This indicates that the deceased was most likely a resident of this city or a surrounding city, who had lived in the city for a long time and had refined dietary habits," Zhang Kai analyzed. "Combined with the locksmith's description that the deceased had a key made and a wallet bought near the North Third Ring Road three months ago, and said that he lived in a community near the northern suburbs, it further indicates that the deceased's activity range was mainly in the northern suburbs area."

Zhang Kai immediately informed Wang Shuai of the test results: "Team Leader Wang, according to our anthropological examination, the deceased is most likely a resident of this city or a surrounding city, who has lived in the city for a long time, has refined dietary habits, and whose activity range is mainly in the northern suburbs. You can focus on investigating males who have recently gone missing in the northern suburbs, aged between 38 and 42, and who are engaged in mental or light physical labor."

Upon receiving the news, Wang Shuai immediately adjusted the direction of the investigation, leading his team to review and compare recent missing persons registered at all police stations in the northern suburbs. However, the investigation did not go smoothly. There are five police stations in the northern suburbs, and a total of 12 males have been recently registered as missing, four of whom are between 38 and 42 years old. The team contacted the families of these four missing persons one by one to verify their identities and characteristics, but after comparison, the height, weight, and clothing habits of these four missing persons did not match the deceased, ruling out a possible match.

"Teacher Zhang, we checked the missing persons list in the northern suburbs based on the characteristics you provided, but we didn't find a match," Wang Shuai reported to Zhang Kai over the phone. "Could the deceased be an unregistered missing person, or a migrant worker with no relatives in the city?" Zhang Kai pondered and said, "That's possible. If he was a migrant worker who didn't register for temporary residence in the city and no relatives reported him missing, it would be very difficult to find him through the missing persons system. In this case, we can only rely on physical evidence from the scene and further investigations to find clues."

Over the next few days, Zhang Kai and Xiao Lin continued to examine the deceased's samples in detail, trying to find more clues. They conducted a detailed compositional analysis of the fiber samples from the deceased's clothing, confirming that the white shirt was made of pure cotton, the black trousers were made of polyester, and the black jacket was made of a wool blend—consistent with the composition of the black fibers found around the body by the forensic department earlier. However, these are all common clothing materials, and the brand or purchase channel of the clothing could not be determined through fiber composition.

They also conducted toxicology tests on the remaining components of the deceased's stomach contents, ruling out the possibility of poisoning by common toxins; and tested the deceased's blood samples for alcohol and drugs, finding no alcohol or prohibited drugs, indicating that the deceased had not consumed alcohol or taken any medication before death. These test results further confirmed that the cause of death was hemorrhagic shock, ruling out other accidental or arsonist causes, but they did not help in identifying the deceased or identifying suspects.

"Professor Zhang, we've done all the tests we could, but we still haven't found any new clues," Xiao Lin said helplessly, looking at the test report. "The deceased is like a 'ghost,' with no identification information or social records. What should we do?" Zhang Kai also felt somewhat helpless. In all his years of practice, this was the first time he had encountered a deceased person whose identity was completely unconfirmable. "Let's review all the test data and autopsy records again, and see if we've missed any details. Sometimes, the most inconspicuous detail might be the breakthrough."

The two reviewed all the examination data, checking every piece of data from the external examination of the body, every discovery during the autopsy, and every result of the sample examination. When they came to the dental examination record of the deceased, Zhang Kai suddenly stopped: "Xiao Lin, look here. The deceased's upper right second molar has an extremely tiny filling. The filling material is resin, and the filling process is very delicate."

Xiao Lin leaned closer to examine it: "Teacher Zhang, this filling is indeed very small. We only noticed that the tooth had no cavities before, and we didn't examine the filling closely. What does this mean?" Zhang Kai said, "Although resin filling materials are common, this kind of delicate filling technique is not something that ordinary small clinics can do. It was most likely performed by a dentist from a regular dental hospital or large dental clinic. Moreover, resin fillings are relatively expensive, and combined with the deceased's dietary habits, it indicates that the deceased had a certain economic foundation and was not a low-income worker."

This discovery invigorated the two men. Zhang Kai immediately said, "We can begin our investigation around this resin filling!" (End of Chapter)