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

He used a high-definition camera to take pictures. "The upper layer has arc-shaped lines, and the lower layer has a faint bucket-shaped pattern. It needs to be separated by computer." There was a half-burnt cigarette butt in the ashtray on the dashboard. When the saliva stain on the filter was sampled, Yang Lin suddenly found a short black hair about 6 centimeters long stuck to the edge of the cigarette butt, with a hair follicle at the root.

“There are impact marks on the left rear wheel arch of the vehicle,” Yang Sen said, using a paint thickness gauge. “The paint thickness here is 3 micrometers thinner than other parts, the primer is exposed, and the attached red particles are preliminarily identified as iron oxide, which may have been left from a collision with the red vehicle.” He used a silicone mold to reproduce the impact marks. “The marks are arc-shaped with a radius of 5 centimeters, which is consistent with the wheel arch characteristics of a small car.”

Yang Lin's investigation has extended to the elevator entrance. On the stainless steel door handle, he extracted three clear fingerprints, one of which overlapped with the whorl-shaped fingerprint feature points of the Passat driver's seat outer handle by 80%: "It may be the deceased's, but more than 16 feature points need to be compared to confirm." The elevator car's surveillance camera was angled too low, only capturing the toes, so he asked the technicians to adjust the angle, "Focusing on capturing footage from 11 pm last night to 1 am this morning, especially people wearing size 42 rubber-soled shoes."

By the fourth hour of the investigation, the evidence bags had reached number 37. Yang Lin sat on the investigation box, organizing the list: "12 biological samples (including 8 suspected bloodstains, 2 hairs, and 2 saliva stains), 9 trace evidence samples (3 fibers, 2 glass fragments, and 4 paint powders), 7 fingerprint samples (3 of which are incomplete), 2 footprint models, and 1 silicone mold of vehicle impact marks." He looked up at Yang Sen, "No evidence was found that directly points to the suspect; all samples require further processing in the laboratory."

Yang Sen was disassembling the seatbelt buckle of a Passat: "There is a trace amount of skin tissue inside the buckle, making DNA extraction difficult," he said, placing the buckle into a sterile container. "It needs to be extracted using the Chelex-100 method, and it may take 48 hours to get the results." He pulled up the vehicle's GPS record: "At 11:07 pm last night, the vehicle stopped at a building materials market in the suburbs for 23 minutes, then returned to the community, entered the garage at 0:42 am, and has not moved since."

The voice-activated light on the garage ceiling suddenly flashed, and Yang Lin's flashlight beam swept across the pipes in the ceiling: "There's a fresh scratch here," he measured with a tape measure, "25 centimeters long and 3 centimeters wide. The dust has been rubbed off, revealing the metallic color." When he took a sample, he found several strands of dark blue fibers, similar in shape to the fibers on the corner of the deceased's clothing, but different in thickness. "They may have been left by the suspect when he climbed the pipes. We need to do a fiber transfer experiment."

During the final examination of the body in its original location, Yang Lin used a vacuum cleaner to collect trace particles from the ground: "We found biological particles that resemble diatoms," he observed under a microscope. "The shells have radial patterns, which may have come from outdoor soil, but we need to compare them with the diatoms in the deceased's lungs to confirm whether they were inhaled before death." Yang Sen then inserted an endoscope into the Passat's exhaust pipe. "There was a small amount of carbon particles accumulated on the inner wall, and no abnormal attachments were found, but the soil sample from the edge of the tailpipe needs to be analyzed for composition and compared with the soil database of the surrounding area."

While organizing the investigation equipment, Yang Lin's camera memory card was already full of 876 photos. Yang Sen categorized all the evidence into "biological," "trace evidence," and "trace material," and labeled them with barcodes: "The fiber sample will be sent for scanning electron microscopy analysis, the shoe print model will be used for stride feature calculation, and the fingerprint sample will be entered into the automatic comparison system." He looked at the items on the list, his brow furrowing slightly, "The most crucial ones are still the DNA typing of the overlapping fingerprint and the suspected bloodstain; these two results may take three days."

After listening to the report at the garage entrance, Lu Chuan took the investigation summary report: "It's normal that there are no major breakthroughs." His finger traced the record of "scratches on the red vehicle." "These fragmented clues can only be connected with the support of laboratory data." He looked at the high-rise buildings in the community. "Notify the technical department to prioritize the processing of biological samples. We're going to meet with Li Wei, the one who drives the red Civic."

As Yang Lin and Yang Sen loaded the last evidence box into the police car, the garage's motion-activated lights went out again. In the darkness, the marked and sampled traces seemed to still be silently telling their story—the origin of the silvery-white fibers, the owner of the overlapping fingerprints, the matching vehicle with the red particles. These answers were hidden in the laboratory equipment that was about to be activated, waiting to be revealed scientifically to uncover the secret that happened in the garage in the early morning.

The stainless steel table in the autopsy room gleamed coldly. As Zhang Kai put on his double-layered latex gloves, the creases on his fingertips were particularly clear under the light. "The deceased was male, around 45 years old," his voice came through his mask, carrying a metallic quality. "Begin the external examination." Assistant Xiaolin placed the measuring tape at the corpse's ankle; the caliper reading stopped at 3.2 centimeters: "The ligature mark is 3.2 centimeters wide and 0.7 centimeters deep, with epidermal abrasion and subcutaneous bleeding at the edges, consistent with hanging before death, but the irregular shape suggests it may have been caused by a soft cord."

Zhang Kai's fingers traced the parallel scratches on the deceased's forearm: "The epidermis was peeled off in shallow grooves, ranging from 2 to 4 centimeters in length and spaced 0.5 centimeters apart, with obvious signs of life," he said, picking up the damaged skin with tweezers. "The dermis shows neutrophil infiltration, indicating resistance injuries formed before death." When the scalpel cut open the chest and abdomen, the subcutaneous fat appeared pale yellow and was 1.8 centimeters thick: "The adipose tissue was evenly distributed, with no abnormal proliferation, suggesting good nutritional status."

“The chest cavity is open,” Zhang Kai announced the dissection steps, the blade moving along the intercostal spaces. “Both lungs are of normal volume, soft in texture, and dark red in color when cut; a pale red foamy fluid oozes out when squeezed.” He cut open the pulmonary artery, finding no thrombus within the vessel: “Pulmonary embolism is ruled out as the cause of death.” When the heart was removed, the coronary arteries on the surface were clearly visible: “The left anterior descending artery has grade II atherosclerosis, with 30% stenosis in the lumen, which does not constitute a fatal lesion.”

Xiao Lin took notes: "There are pinpoint hemorrhages scattered under the epicardium." She observed with a magnifying glass: "The left ventricular wall is 1.2 cm thick, and the myocardial fibers are neatly arranged without any rupture or necrosis." Zhang Kai cut open the right atrium, and the blood inside was dark red and did not coagulate: "The blood does not coagulate, which is consistent with the blood characteristics of death by asphyxiation."

As the scalpel turned to the neck, Zhang Kai moved with extreme caution. "No fractures were found in the greater horn of the hyoid bone or the superior angle of the thyroid cartilage," he dissected the neck muscles. "There was bleeding deep within the sternocleidomastoid muscle, measuring approximately 4 x 5 cm. No enlarged cervical lymph nodes were observed." The thyroid gland was reddish-brown and of medium consistency: "It measures approximately 4 x 2 x 1.5 cm; no nodules or tumors were found on the biopsy." (End of Chapter)