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

The leather cover of the steering wheel was torn, exposing the sponge inside. "A few dark brown cotton threads were stuck in the fibers at the torn edge. The twist coefficient was 16.8, which is industrial-grade canvas material." He asked the technicians to extract fingerprint samples. "After using 502 glue to develop the fingerprints, we'll see if we can extract complete fingerprint lines."

Yang Sen made a discovery in the northwest corner of the parking lot, where the weeds showed signs of being trampled. "They were distributed in strips, about 5 meters long," he said, measuring the width with a laser rangefinder, "30 centimeters, consistent with the characteristics of two people dragging them. There were traces of fresh bodily fluids at the broken ends of the weed stems, requiring samples for DNA analysis, but judging from the color, it looked like blood mixed with soil." He followed the drag marks and stopped under an abandoned truck. "There's a black plastic bag here, its opening is open."

The plastic bag contained half a rusty steel pipe, about 60 centimeters long and 5 centimeters in diameter, with dark red stains and grass-green fabric fibers on its walls. "One end of the steel pipe is deformed from an impact," Yang Sen measured the degree of deformation with a ruler, "The curvature perfectly matches the dent in the van's exhaust pipe, so it should be the weapon that hit the exhaust pipe." He had the technicians put the steel pipe into an evidence bag, "There are traces of wiping on the inner wall, but the remaining fibers are consistent with those on the steering wheel, all dark brown coarse cotton thread."

Wang Shuai helped Lao Li to his feet. The wind from the parking lot carried a stench, and the barking of stray dogs could be heard in the distance. "What are the distinctive features of that white sedan?" He drew the sedan's general outline on the notebook. "For example, the model, whether there are any stickers or damage?" Lao Li shook his head: "It was too dark to see clearly, but I remember there was a roof rack on the roof, and the rear bumper was a bit crooked, like it had been hit."

Yang Lin's investigation light shone on the trunk lock of the van, revealing signs of tampering in the lock cylinder. "The misalignment angle of the pins is larger than that of the door lock," he observed with a magnifying glass, "indicating that more force was used. Preliminary testing of the metal powder on the lock body shows that it contains zinc and copper, likely from some kind of homemade lock-picking tool." He had the technicians open the trunk, and an even stronger stench of decay wafted out. Several long black hairs were stuck in the trunk mat, "about 30 centimeters long, with hair follicles at the roots, from which DNA samples can be extracted."

As the last rays of sunlight disappeared at the end of the parking lot, Yang Lin and Yang Sen's investigation notebooks were filled with 34 new clues. They sorted and packed all the samples: dark brown cotton fibers, plaster models of tire tracks, steel pipes, black plastic bags... each item was meticulously labeled. "Although we found quite a few traces, we lack physical evidence that directly points to the murderer," Yang Lin said, closing his notebook, his voice tinged with fatigue. "The size 42 shoe print and the white sedan are new leads; we need to retrieve and investigate surveillance footage from the surrounding roads."

Lu Chuan's walkie-talkie suddenly crackled to life. The technical team had made a discovery at the location where the white sedan had been parked. "There's a patch of light green paint residue on the ground," the technician's voice was excited. "Preliminary testing shows it matches the original paint composition of a certain domestic SUV, likely a Haval H6." Lu Chuan immediately gave the order over the walkie-talkie: "Check all white Haval H6s with local license plates from the last three days, paying particular attention to vehicles with damaged rear bumpers or roof racks!"

Wang Shuai took one last look at the blue minivan. Through the hole in the window, a corner of a dark blanket peeked out, vaguely revealing the huddled silhouette inside. He knew the next step was to cordon off the scene and wait for the technical team to conduct a more detailed investigation, while simultaneously expanding the search area for traces of the white Haval H6. But now, at least in the initial investigation, they had already caught some clues left by the killer. These scattered clues would eventually piece together the outline of the truth in the darkness.

Lu Chuan's rubber boots crunched over the gravel at the edge of the parking lot, the static from his walkie-talkie mingling with the distant barking of dogs. "Expand the radius to 50 meters, centered on the van," he said, tracing an arc on the ground with his toes, his glow stick leaving a green trail in the twilight. "The drainage ditch outside the wall, the abandoned oil tank area on the east side, and that area with weeds taller than 1.2 meters—scan them all with a 3D scanner." He patted Yang Lin on the shoulder; the words "Site Investigation" on the survey kit gleamed coldly under his headlamp. "Bring the newly acquired ground tomography scanner; see if there's any buried evidence."

Yang Lin was crouching behind the right side of the van, setting up a 3D laser ground scanner, the tripod legs sinking into the soft soil. "Yang Sen, calibrate the coordinate system," he said, staring at the point cloud model on the screen. "Set the rear axle of the van as the origin, and point the X-axis towards the parking lot gate." The instrument emitted a high-frequency beeping sound, millions of point cloud data points piling up on the screen every second, gradually outlining the terrain within a 20-meter radius. "Look at the ground in the oil tank area," he zoomed in on the abnormal area on the model, "there's a 2x3 meter subsidence zone, with a subsidence of about 5 centimeters, it might have been recently excavated."

Yang Sen carried the Raman spectrometer around to the wall, pointing the portable device's probe at the unidentified liquid in the drainage ditch. "Benzo[a]pyrene characteristic peak detected, wavenumber 3050 cm⁻¹," he announced, an orange warning box appearing on the instrument's display. "Concentration 1.2 μg/L, belonging to diesel combustion residue, but the sediment thickness indicates it was left three months ago, inconsistent with the time of the incident." He collected samples with a sterile pipette. "The moss on the ditch wall shows signs of crushing, and the fiber sample indicates it's made of polypropylene, consistent with supermarket shopping bags, likely discarded by a scavenger."

“The 3D scan shows a breach in the wall,” Yang Lin’s voice came from beside the scanner. He adjusted the lens focus, and the steel bars at the breach appeared as bright red on the model. “The gap is 80 centimeters wide and 1.5 meters high. Dark brown fibers are stuck in the concrete debris at the edge, and their reflectivity is consistent with the coarse cotton thread we found earlier.” He asked Yang Sen to take pictures with a multispectral camera. “At the 450nm wavelength, the fluorescence intensity of the fibers is 30% lower than that found inside the car, indicating a higher degree of degradation, possibly from an earlier period.”

Yang Sen operated a portable X-ray fluorescence spectrometer, the probe aimed at the soil outside the wall. "A lead peak was detected, at 120 mg/kg," he said, comparing it to the soil background database. "This is more than four times the surrounding average, but the isotope ratio indicates industrial pollution, not recent human dumping." He scanned the subsidence zone with ground-penetrating radar; the waveform on the screen showed a regular layered structure. "No metallic foreign objects were found. The subsidence was caused by natural compaction, not excavation." (End of Chapter)