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

The fence surrounding the unfinished building was made of blue sheet metal, with numerous holes and cracks due to rust. Yang Lin focused his attention on the damaged areas, carefully examining the edges of each gap: "Yang Sen, look at this gap. There are fresh friction marks on the edge, and a small amount of gray fiber remains on the sheet metal, likely left by frequent recent entry and exit." He used tweezers to extract a small fiber sample and placed it in an evidence bag labeled "Outer Periphery-001," adding, "This is marked as an outer periphery fiber sample for later testing and comparison."

Yang Sen used his camera to take photos of the gap from multiple angles, including close-ups of the marks and panoramic views of the surrounding environment: "This gap is about 1.2 meters wide, located on the northwest side of the fence, about 20 meters from the main entrance of the unfinished building. It's the easiest gap to enter and exit. I'll check the other gaps for similar marks." After investigation, the edges of the other four damaged gaps showed signs of old rust, with no fresh friction or fiber residue. It was initially determined that the suspect and the deceased most likely entered the scene through the northwest gap.

The two then surveyed the area from the inside of the fence to the main entrance of the unfinished building. The area was covered in weeds about 50 centimeters tall, interspersed with construction debris such as steel bars and cement blocks. Yang Lin turned on his survey light and slowly moved along possible routes: "Focus on checking for signs of fallen weeds and footprints on the ground, paying attention to distinguishing between the footprints of the person who reported the incident and those of homeless people." Yang Sen operated a laser rangefinder to measure and record the distances and orientations of the area, drawing a preliminary site map.

"There's a set of fresh footprints here!" Yang Sen discovered something unusual in the weeds about 15 meters from the gap on the northwest side. The two immediately approached and crouched down to examine them closely. The footprints were located on a relatively flat patch of muddy ground. Due to recent rainfall, the ground was quite damp, and the footprints were relatively well-preserved. "The footprints are from rubber-soled shoes, about size 42, with horizontal stripes. There are obvious signs of wear at the front. The stride is about 75 centimeters, and the stride angle is 15 degrees, indicating that they were left by an adult male." Yang Lin measured the various dimensions of the footprints with a tape measure, while Yang Sen took close-up photos of the front and side of the footprints with a camera. "The direction of these footprints is towards the main entrance of the unfinished building, ruling out the person who reported it—the person who reported it was wearing cloth shoes, size 40, with a completely different pattern."

Yang Lin took out the footprint extractant and plaster powder and began to make a footprint model: "First, spray a fixative to prevent the footprint from deforming during the extraction process." He evenly sprayed the extractant on the surface of the footprint, and after it dried, he slowly poured in the mixed plaster powder. "The plaster powder should be spread evenly, with a thickness of at least 2 centimeters, to ensure that the footprint details can be completely replicated." Afterwards, the two continued to search the surrounding area and found three more footprints with the same pattern, distributed in a straight line with even spacing, further confirming that the owner of the footprints had entered the unfinished building with a purpose, rather than being a homeless person wandering around randomly.

After completing the extraction of footprints from the outer perimeter, the two arrived at the main entrance of the unfinished building. The glass door at the main entrance was already broken, with glass shards and rust remaining on the door frame. Yang Lin shone a searchlight on the inside of the door frame: "There are fresh wiping marks on the door frame, which may have been wiped by the suspect or the deceased to avoid being scratched by the glass when entering." He used a fingerprint brush to apply a small amount of black powder and gently brushed over the wiping marks. "Partial fingerprint lines appeared, but they were incomplete; they should be incomplete fingerprints." Yang Sen immediately used transparent fingerprint tape to extract the fingerprint and placed it in an evidence bag labeled "Main Entrance-001".

Upon entering the unfinished building, a musty and dusty smell assaulted the senses. The first-floor lobby was spacious and empty, with construction debris and discarded building materials scattered on the floor. The walls exposed steel bars and cement layers, with numerous signs of water seepage. Yang Lin activated a multi-band light source, adjusting the wavelength to 450 nanometers, to inspect the lobby's floor and walls: "The first floor is a transitional area; focus on checking for bloodstains and drag marks." Yang Sen, meanwhile, photographed and documented the lobby's structure and layout, marking the location of the stairwells—there were two staircases, one on the east side and the other on the west side of the lobby, both concrete staircases without handrails.

The two first examined the east staircase. The steps were covered with a layer of dust about 1 centimeter thick, with a few messy footprints, mostly from cloth shoes and worn-out rubber shoes, which they determined to be left by a homeless person. "The footprints on the east staircase are all old, with no fresh footprints or bloodstains, so they are most likely not the route the suspect took," Yang Lin said. The two then turned to the west staircase, and as soon as they reached the top, they noticed something unusual.

On the dusty steps of the west staircase, there was a set of clear, fresh footprints, perfectly matching the size 42 striped rubber-soled shoe prints previously found inside the fence. "These footprints are in an upward direction, extending from the first floor to the third floor, indicating that the suspect went up to the third floor from the west staircase," Yang Sen said, examining the footprints upwards. "Each step has complete footprints, without any signs of jumping or pausing, suggesting the suspect was in a relatively stable state at the time."

Yang Lin shone his survey light on the surface of the steps and found a tiny, dripping mark on the fifth step: "Yang Sen, look here! It looks like blood!" He adjusted the angle of the light; the mark appeared dark red, circular in shape, about 0.5 centimeters in diameter, with neat edges. "Conduct a preliminary test with benzidine reagent." Yang Sen took out a reagent bottle from the survey kit, dripped a small amount of reagent onto the mark, and after about 10 seconds, the mark turned blue. "Confirmed to be blood!" Yang Lin noted, "Marked as West Staircase-001 bloodstain sample, located on the fifth step of the west staircase, 1.2 meters above the ground, dripping vertically downwards, indicating blood dripped during walking."

The two continued their investigation upwards and found three more similar bloodstains on the 12th, 18th, and 25th steps of the west staircase. The size and shape were almost identical to the bloodstains on the 5th step, arranged in a straight line with a spacing of about 1.5 meters, perfectly matching the direction of the footprints. "The even spacing of these bloodstains indicates that the suspect was walking at a steady pace, without any signs of running or panic," Yang Lin analyzed. "Combined with the location and shape of the bloodstains, it's highly likely that the suspect had blood on him, which dripped naturally during his walk. However, it cannot be ruled out that the suspect carried the victim's blood here."

At 9:58 AM, the two arrived at the third-floor stairwell. The third floor's structure was similar to the first floor, an open space with several undivided room frames in the middle. The walls and floors were unfinished concrete, with scattered scrap wood and steel bars. The body, as described by the caller, was located within a room frame on the north side of the third floor, approximately 15 meters from the stairwell. (End of Chapter)