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

As Wang Shuai closed the notebook, Li Fenghuai was still reciting the story of the man in the suit. "If he hadn't gotten into trouble, where would he be now?" The shepherd's voice was filled with regret, his cane leaving messy marks on the ground. Wang Shuai noticed some black powder on the cuffs of his sheepskin coat. After taking a sample, he found it was charcoal ash—probably picked up when he was near the fire while calling the police, and its composition matched the ash found at the scene.

On the highway outside the police cordon, the police car's engine was still idling. Lu Chuan gazed at the morning mist deep in the mountain valley and suddenly said to the officer beside him, "Check recent missing persons, focusing on men wearing dark blue windbreakers and silver watches, and..." He pointed to the pearl earring, "...check all Tiffany boutiques in the city and see who has recently bought this earring." The mountain wind rustled through the treetops in the distance, carrying the acrid smell of burning wood, as if hiding the name swallowed by flames, waiting to be picked up from the ashes.

Lu Chuan continued to instruct Yang Lin and Yang Sen to expand the search area and conduct a wider investigation in the vicinity in an effort to find more clues.

The morning mist around the valley gradually dissipated. Yang Lin moved up the slope on his surveying treadmill, the beam of his surveying light drawing bright lines through the grass. "Expand the radius by fifty meters," he said into the walkie-talkie, the anti-slip treads of his boots carving neat diamond-shaped marks in the wet mud. "Focus on checking the soil structure beyond the burn marks, and look for non-native vegetation debris." Yang Sen was squatting under an old locust tree at the valley entrance, the blue light of his footprint light illuminating a circle of blurry shoe prints. He used a scale to pinpoint the forefoot of the print: "Senior, there's a fragmented size 42 shoe print here, matching the pattern of the footprints next to the corpse, but the pressure distribution is different—the forefoot pressure is 8% lower than before, like a gait after carrying a heavy load."

As Yang Lin walked over, dew dampened the cuffs of his survey uniform. He bent down to examine the raised soil around the shoe print: "15-degree stride angle, outward gait, consistent with weight-bearing walking." He pulled out a multi-band light source and swept it around the shoe print; a pale blue fluorescence lit up on the grass. "Suspected oil stains found; take a sample for testing." Yang Sen had already opened the evidence bag and used a sterile cotton swab to collect soil from the fluorescent area: "Look, senior, there's a 0.3-centimeter parallel scratch along the heel edge of this shoe print, probably caused by a small stone stuck in the sole. It matches the characteristic damage of the one next to the body."

The two followed the footprints towards the hillside. The bushes on the slope showed clear signs of being trampled, and fresh cuts from broken branches were still oozing sap. "The bush fibers broke through a tensile fracture," Yang Lin said, picking up a broken branch with tweezers. "It didn't fall naturally; it was forcibly pried open. There are remnants of pale blue fabric fibers at the break, which preliminarily match the fiber composition found on the corpse's wrist." Yang Sen opened the footprint analysis system and entered the shoe print data: "Based on a stride length of 70 cm and a stride width of 12 cm, the suspect's height is estimated to be between 172-175 cm, and his weight approximately 70 kg. This is consistent with the analysis of a weight-bearing gait."

In a hollow on the hillside, Yang Sen's metal detector suddenly beeped. He crouched down and brushed aside the fallen leaves, revealing a rusty iron nail in the sunlight, a black nylon thread wrapped around its head. "This is a construction cement nail, 5 centimeters long," Yang Sen said, bringing a magnet close to the nail, attracting iron filings from the thread. "The surface is moderately rusted, with three layers of rust, indicating it's been exposed to air for at least three months, but the fresh scratches on the head suggest it was recently touched." Yang Sen tested the surrounding soil with pH paper: "The soil pH is 7.2, slightly neutral, suitable for metal preservation. This nail is located 120 meters from where the body was found, not on the main footprint line, so it was likely dropped unintentionally by the suspect."

The two continued towards the ridge. Yang Lin suddenly stopped in a patch of withered yellow grass, his searchlight beam focusing on a clump of black ash. "Isolated ash in the non-combustible area," he said, measuring the ash with a ruler. "It's about 8 centimeters in diameter, irregularly shaped, containing unburnt charcoal particles, 0.5-1 millimeters in diameter, consistent with the charcoal composition of the fire next to the body." Yang Sen used an anemometer to measure the wind speed: "Southeast wind, level two. Judging by the speed of the fire's spread, this isolated ash must have fallen here when the suspect moved the source of the fire, indicating he stayed here after committing the crime."

On the rocks at the ridge, there was a fresh scratch mark, with grayish-white stone powder accumulated in the crevices. Yang Lin shone the scratch mark with a sidelight: "A unidirectional linear scratch mark, 15 centimeters long, 0.3 centimeters deep at the beginning and 0.1 centimeters shallow at the end, consistent with the characteristics of oblique friction from a hard object." He took out a silicone mold and carefully covered the scratch mark: "Extracting three-dimensional traces, it may have been caused by a tool carried by the suspect." Yang Sen found half a cigarette butt next to the rock; the lip print on the filter was blurred, but the degree of burning of the tobacco indicated that it had been deliberately extinguished: "A Zhonghua brand cigarette, the cigarette butt is 3.2 centimeters long, moderate smoking intensity, DNA typing on the filter is being tested, and the soil around the cigarette butt is slightly compacted, indicating that the suspect had stood there smoking."

On the way back down the mountain, Yang Sen's footprint light detected something unusual under a patch of ferns. "There's a faint indentation here," he said, parting the ferns to reveal grass stems lying flat in the same direction. "It's about 0.2 square meters, oval-shaped, with traces of rotation around the edges, like someone placed a heavy object here." Yang Sen used a soil hardness meter to measure the center of the indentation: "Hardness value 65, 20 higher than the surrounding soil, consistent with placing an object weighing over 10 kilograms." He suddenly remembered something, "Could it be a gasoline drum? The suspect might have temporarily stored accelerants here."

Back at the edge of the valley, the sun was already high in the sky. Yang Lin found several white crystals in the unburned soil extending beyond the burnt area. “Examine them under a polarizing microscope,” he said, handing Yang Sen a handful of crystals. “Refractive index 1.45, hexahedral structure, possibly table salt—but this place is sparsely populated, how could there be table salt?” Yang Sen immediately took a sample: “Could it be an additive in the combustion accelerant? Or food scraps carried by the suspect?” Yang Lin shook his head, pointing to the soil color around the crystals: “The soil is light brown, while table salt would make the soil appear white; this is more likely some kind of industrial salt, commonly found in antifreeze or herbicides.”

As the two sat on the rocks organizing their investigation records, the mountain breeze carried the sweet scent of pine needles past their ears. "The clues we've found so far can piece together part of the crime," Yang Lin said, drawing a trajectory on the ground with a twig. "The suspect, wearing size 42 sneakers, carried accelerant and pine branches to the valley, made contact with the victim, set the fire, and then retreated along the mountainside carrying the load. He stopped at the ridge to smoke, dropping a spark and a nail along the way." (End of Chapter)