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

“The valve on the east side of the oil tank has fresh signs of turning,” Yang Lin’s headlamp swept across the rusty valve disc. Under the 365nm ultraviolet light from the multi-band light source, half a blurry fingerprint appeared on the disc. “The ridge spacing is 2.3mm, and the central pattern is loop-shaped, but the amount of sweat crystallization at the edge is insufficient to extract complete feature points.” He used a silicone rubber mold to make a copy. “The aging of the valve’s sealing gasket indicates that it has not been opened for at least six months. This fingerprint was probably left by an unauthorized person.”

Yang Sen deployed his infrasound detector in the weeds. As the low-frequency sound waves propagated through the air, waveform fluctuations appeared on the instrument's display. "There's an abnormal signal in the 10-20Hz band," he adjusted the gain knob. "The source is an abandoned truck about 30 meters to the northwest." As the two men pushed aside the waist-high weeds to get closer, they found a stray cat in the truck's cab. The infrasound was generated by the cat scratching the metal. "A false alarm," Yang Sen said, his trouser legs covered in burrs as he packed up the equipment. "However, the straw in the truck bed showed signs of being disturbed. Fiber samples showed it was mixed with dark brown cotton thread, but the twist coefficient was 15.2, 1.6 lower than the straw inside the truck, indicating it's not from the same batch."

Yang Lin's ground tomography scanner made a discovery at the edge of the parking lot. The grayscale image on the screen showed an irregular object 30 centimeters underground. "Approximately 30 x 20 centimeters in size, density 1.2 g/cm³," he calculated the parameters, "It's probably a metal or plastic container." Technicians carefully dug with a shovel, and half an hour later unearthed a rusted tin box containing only some yellowed newspapers dated 2021. Fiber analysis showed no components related to the case. "A waste of effort," Yang Lin wiped the sweat from his brow, "This box has three layers of rust; it's been buried for at least two years."

“Look at this tire track,” Yang Sen suddenly called out to Yang Lin, who was packing up his equipment. He scanned the ground with a laser profilometer. “225/65R17 specification, symmetrical tread pattern, matching the original tire parameters of the Haval H6.” But after comparing the tire wear characteristics, his brow furrowed. “The depth difference of the longitudinal grooves is 0.3mm, which is less than the wear of the suspect vehicle. It should be left by a different vehicle of the same model. Moreover, the tire pressure shows that it is unloaded, which does not match the state we are looking for, ‘possibly carrying a corpse.’”

Yang Lin used a multispectral camera to photograph the drag marks extending beyond the wall. Under the 800nm ​​near-infrared band, the direction of the fallen grass stems showed a continuous linear characteristic. "It extends from the edge of the parking lot all the way to the national highway 50 meters away," he measured the angle of the falls, "with an average deviation of 35 degrees from the vertical, consistent with the force characteristics of a two-person drag." However, at the end of the drag marks, Raman spectroscopy detected skin tissue fragments, and preliminary DNA typing indicated that they belonged to a woman, contradicting the male characteristics of the body inside the car. "It might have been left by a homeless person; the nearby shelter said that scavengers often frequent this area."

By the time the results from the portable gas chromatography-mass spectrometry (GC-MS) came out, night had already fallen over the entire parking lot. "The steel pipe in the black plastic bag has vegetable-based residual grease on its surface," Yang Sen said, looking at the chromatographic peaks on the screen. "The ratio of palmitic acid to stearic acid is 3:1, which is common rapeseed oil, not engine oil or diesel. It's likely contaminated cooking oil from the murderer's home." But this finding lacked specificity and couldn't narrow down the investigation.

Yang Lin's 3D scanner finally completed a panoramic scan with a 50-meter radius. The point cloud model rotated on the laptop, the dense dots forming a digital twin of the parking lot. "All the anomalies have been marked," he zoomed in on a bright spot in the tanker area, "This 10-centimeter-diameter metal reflector is actually an abandoned car license plate, registered in a neighboring city, and cancelled three years ago." As he turned off the model, the screen reflected the tired faces of the two men. "Fibers, tire tracks, fingerprints, drag marks—all the findings lacked direction; there was no physical evidence directly linking to the murderer."

As Yang Sen packed up his equipment, the ground-penetrating radar cables became tangled. "The infrasound detector recorded anomalies, besides the cat, including the sound of flowing water outside the wall," he untangled the knot. "Raman spectroscopy analysis revealed dark brown fibers, and infrared spectroscopy showed it was a cotton-polyester blend, 65% cotton. This kind of industrial canvas is common in local building materials markets; at least 20 stores sell it." He kicked at the gravel under his feet. "The most useful thing might be that incomplete fingerprint. We can process it with fluorescence in situ hybridization; maybe we can extract more feature points."

As Lu Chuan's walkie-talkie crackled with questions, Yang Lin was packing up the last piece of equipment. "After expanding the investigation area, no major clues were found," his voice was slightly distorted by the electrical current, "but we obtained a complete 3D model of the scene and 23 trace evidence samples. We'll report back after a systematic analysis." He glanced up at the national highway outside the wall, the beams of headlights flowing in the night. "At least we've ruled out the possibility of burying evidence. The murderer should have left directly after dumping the body, without lingering."

The moment Yang Sen locked the survey box, a distant oil tank suddenly clanged, a sound of metal deformation caused by thermal expansion and contraction. "We can apply for drone aerial surveying tomorrow," he said, rubbing his aching shoulders. "We'll scan the surrounding 1 square kilometer area to see if we've missed any vehicle tracks." Yang Lin nodded. As he started the SUV, the dashboard showed midnight. The stench of decay wafted through the parking lot into the car window. The scanned, analyzed, and marked traces eventually vanished into the deeper darkness, as if they had never existed.

While Yang Ling and Yang Sen were expanding their on-site investigation, the body had already been transported back to the Criminal Investigation Detachment.

Forensic pathologist Zhang Kai has begun performing an autopsy to determine the time and cause of death.

The stainless steel table in the autopsy room gleamed coldly under the operating lights. When the body was brought in, the dark blue body bag was still covered with grass seeds from the parking lot. Zhang Kai, wearing double-layered rubber gloves, felt a mixture of putrid fumes and diesel fuel waft out the moment his fingertips pinched the zipper of the body bag. "Record: Male cadaver, preliminary assessment of time of death exceeding 72 hours," his voice sounded muffled through his mask. His assistant, Kobayashi, wrote neatly on the autopsy record. "A network of putrefied veins is visible on the body surface, most prominent in the chest and abdomen; the greenish tinge has spread to the proximal extremities."

The operating light beam focused on the corpse's neck. With the help of his assistant, Zhang Kai used hemostats to lift the loose skin, and putrefactive fluid flowed through the gaps in the subcutaneous tissue. "There's a 5x3cm skin defect on the left side of the neck," he said, his ruler positioned at the edge of the defect, measuring the skin loss on the neck. (End of Chapter)