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

Yang Sen mixed the mud with plaster powder. "These kinds of shoe prints won't leave a mark on hard ground. Luckily, it rained these past few days, and the mud layer is just the right thickness to set." He suddenly pointed to the grass clippings at the edge of the shoe print. "There's some cement dust mixed in. Maybe the murderer works in the construction industry."

Expanding the search area to 500 meters, Yang Sen discovered three cigarette butts stacked together behind a large rock. "Hongtashan cigarettes, 10mg tar," he said, placing the butts into an evidence bag with tweezers. "The saliva stains on the filters are still fresh; DNA testing should yield results." Next to the cigarette butts, there was a slumping mark on the ground, with flattened dead leaves, measuring approximately 1.2 x 0.6 meters. "The murderer stayed here for at least half an hour, smoking three cigarettes, possibly observing the surroundings." Yang Lin suddenly noticed a fluorescent reaction on the grass at the edge of the mark. "Shine a UV light on it; there are oil stains."

Under the ultraviolet light, the oil stains on the grass showed pale blue spots, shaped like half a handprint. "It's machine oil," Yang Lin said, dipping a test strip into the sample. "Component analysis needs to be done back in the lab, but judging from the color and viscosity, it looks like diesel or engine oil." He suddenly remembered the victim's jacket. "There were similar oil stains on the cuffs of the body. Could it be that the murderer had physical contact with the victim?" Yang Sen shook his head, pointing to the stone next to the cigarette butt: "There are friction marks on the stone. The murderer may have rubbed oil from his hands here, which looks more like cleaning marks after committing the crime."

As the two searched westward along the ridgeline, Yang Lin's searchlight stopped at the edge of a cliff. The vines on the cliff face showed signs of being pulled, and several dark green branches hung in mid-air, their ends wrapped in a piece of fluorescent green cloth—the exact same color as the deceased's jacket. "From here to the body's location, the straight-line distance is 120 meters, but the mountain path is a 300-meter detour," Yang Sen measured with a laser rangefinder. "The drag marks end at the cliff edge; it's possible the body was pushed down from here and then dragged into the woods." At the bottom of the cliff, on a pile of rubble, there was a fresh impact mark, the fibers clinging to its edge identical to the cloth on the vines.

“Look at this burn mark,” Yang Lin said, crouching down in a clearing 300 meters from the body. There was a black circle about 80 centimeters in diameter on the ground, with unburnt branches mixed in with the ashes. “The combustion residue test shows gasoline components, so it wasn’t a spontaneous combustion.” In the soil around the black circle, Yang Lin sifted out a metal piece with a sieve. “It looks like the casing of a lighter, with the word ‘ZIPPO’ on it, but the model number is illegible.” On the tree trunks around the clearing, there were several cut marks, 1-2 centimeters deep, like those left by a machete or axe. “The murderer may have started a fire here for warmth, or burned something.”

The investigation continued until noon, and the two investigators had filled their notebooks with 27 clues: the pressure distribution curve of the size 44 work boot print, the warp and weft density of the dark blue nylon thread, the preliminary colorimetric reaction of the machine oil, the brand and model of the cigarette butt, the compositional analysis of the combustion residue... but none of them directly pointed to the victim's identity or the killer's characteristics. "The most troublesome thing is the lack of identification," Yang Lin said, sitting on a fallen log, drinking water and tapping the bottle cap rhythmically on his notebook. "The victim's backpack was ransacked, and the killer may have taken his identification and electronic devices."

Yang Sen was sorting through the evidence bags, the labels numbered from "Scene 01" to "Outer Perimeter 27". "That silver carabiner is a bit strange," he said, pulling out a photo of the evidence. "The inside of the ring is worn, but there are no signs of anything being hung on it, it seems more like it was deliberately placed there." Yang Lin suddenly remembered the vines on the cliff edge: "Could it be that the murderer used the carabiner to tie the body to the vines and lower it down? But the ring doesn't show any signs of weight-bearing, so that doesn't make sense." The two stared at the photo for a long time, but still couldn't find a reasonable explanation.

“The pigeon-toed gait, work boots, machine oil, Hongtashan cigarettes… these clues point to a manual laborer,” Yang Lin drew a profile on the ground with a twig. “Male, 175-180cm tall, working in machinery or construction, familiar with the outdoor environment, possibly with a criminal record—because he was very aware of counter-surveillance and deliberately cleaned up his shoe prints and fingerprints.” Yang Sen added, “But the deceased’s equipment was very professional; the fluorescent green jacket was from a professional outdoor brand, and the backpack’s carrying system was expensive, suggesting he was an experienced hiker. How could these two identities intersect?”

Wang Shuai's voice came through the walkie-talkie: "We've checked the social connections of the person who reported the case, Li Lijun, and there's nothing unusual. His hiking records show that he does come here every week to take photos." Yang Lin turned off the walkie-talkie. "We've ruled out the person who reported the case, but the relationship between the deceased and the murderer is still a mystery." He suddenly pointed to the firebreak in the distance. "There are tire tracks on the firebreak. Could it be that the murderer drove to the vicinity and then transported the body into the woods?" Yang Sen immediately got up. "Let's go take a look. The spacing of the tire tracks and the tire treads might be able to pinpoint the vehicle type."

On the concrete ground of the firebreak, two tire tracks were clearly visible, 1.5 meters apart, with horizontal treads and a depth of 0.2 centimeters. "It's a truck or SUV," Yang Lin measured with a tape measure. "The tire width is 245mm, and the wear is moderate, so it should be a vehicle that's been used for about two years." Next to the tire tracks were several scattered size 44 shoe prints, which perfectly matched the work boot prints next to the body. "The murderer definitely drove here, parked the car on the firebreak, and then dragged the body into the woods on foot." But the tire tracks disappeared at the end of the firebreak, surrounded by an open grassland with no surveillance cameras, making it impossible to track the vehicle's whereabouts.

Back at the body, technicians were performing an X-ray scan on the backpack. "There are no electronic devices in the bag," Yang Sen said, looking at the scan. "There's a metal box, shaped like a jewelry box, but it's locked; we'll have to pry it open back at the lab." Yang Lin suddenly noticed a broken pencil in the side mesh pocket, with a blurry "W" etched on the shaft. "This might be the initials of the deceased's surname, but it's too blurry to be sure." In a compartment at the bottom of the bag, Yang Sen pulled out a sweat-soaked note; the writing was blurred, only the words "Saturday," "ridge," and "see you" were legible.

“All the clues are too fragmented,” Yang Lin spread his investigation notebook on the tree trunk. Sunlight filtered through the leaves, illuminating the words “Unknown male, around 40 years old, 178cm tall.” “No identification, no electronic devices, the only DNA sample came from a cigarette butt, and we don’t even know whose it is.” Yang Sen’s phone suddenly vibrated. It was a preliminary report from the lab: “The fluorescent green fabric’s fiber composition is nylon 66, commonly found in professional outdoor clothing, but without any brand markings; the machine oil sample is preliminarily identified as diesel, consistent with the composition of fuel commonly used in trucks.”

As the two men sat on the fallen log sorting through the evidence, the wind in the forest suddenly picked up, causing the wires of their investigation lights to swing back and forth. (End of Chapter)