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

More and more residents gathered outside the cordon, their voices rising like a tidal wave. Lu Chuan ordered into the walkie-talkie: "Immediately retrieve all surveillance footage from the area surrounding the community and investigate any suspicious vehicles from the night of September 11th; contact the water company to test the water quality for contamination; visit all residents of Building 3, especially those who have shown unusual behavior recently." The sunlight gradually rose, and the stainless steel casing of the water tank reflected a blinding light, as if to completely illuminate the evil hidden in the water.

Yang Lin and Yang Sen's investigation logs already filled two pages, detailing everything from shoe print characteristics and fiber composition to lock marks and cigarette butt brands—every clue pointing to the lurking killer. At this moment, the secret beneath the surface remains unsolved, but as the investigation deepens, the truth will eventually be exposed to the light of day, like a body pulled ashore.

"Expand the scope of the on-site investigation."

When Lu Chuan's instructions came through the walkie-talkie, Yang Lin was squatting next to the water tank's inspection port, taking fingerprints. "Expand the search area to the entire Building 3 and a 50-meter radius around it, focusing on fire exits and underground pipe networks." Amidst the static and the chatter of residents outside the cordon, Yang Lin looked up at the midday sun, which made the stainless steel casing of the water tank scorching hot. "Roger that, we'll start from the fire exits."

Yang Sen followed behind, carrying his investigation bag. The cable of the footprint light left shallow marks on the ground. "These size 44 shoe prints extend from the unit entrance all the way to the fire escape," he said, measuring the distance between the prints with a ruler. "The stride length decreased from 75 centimeters to 70 centimeters, indicating that the suspect slowed down after entering the passage." The iron gate to the fire escape was ajar, with obvious signs of prying on the lock cylinder and some blue paint chips hanging from the edge.

“Look at this door frame,” Yang Lin shone his investigation light on the hinge, where there were fresh scratches on the metal surface. “It was pried open with a flathead screwdriver. The scratches are 0.8 centimeters wide, which matches the pry marks on the water tank lock.” He took out an evidence bag to collect paint debris. “It’s blue nitrocellulose lacquer, and the paint composition is different from that on the water tank’s outer shell. It may have come from the suspect’s tools or clothing.”

The two searched each floor along the fire escape route. At the corner of the staircase, there was a light blue water stain on the concrete floor. "It's water from the water tank," Yang Sen said, testing it with pH paper. "pH 7.2, chlorine content 0.3 mg/L, consistent with the water quality in the tank." There was a half-faded shoe print around the edge of the stain, the forefoot clearly visible. "It's size 44, and there are rust particles embedded in the sole pattern; it must have come from the water tank."

“The suspect likely went up and down the stairs via the fire escape,” Yang Lin stopped on the third-floor platform, where the window faced the side of the water tank. “Look at this windowsill, there are signs of dust being wiped away, and it’s about 40 centimeters wide, just big enough for one person to pass through.” The fiberglass on the windowsill showed blue polyester characteristics, which were exactly the same as those found in the flower bushes. “He may have observed the location of the water tank from here.”

Yang Sen suddenly pointed to a cigarette butt on the stair railing, which matched the Yuxi brand cigarette butt found next to the water tank. "The cigarette butt is 2.8 centimeters long, 0.2 centimeters shorter than the previous one," he said, carefully picking it up with tweezers. "The stronger drag suggests the suspect may have hesitated or been waiting. The saliva stains on the filter are thicker, indicating a higher success rate for DNA extraction." He suddenly leaned closer and smelled it. "It has a faint disinfectant smell, similar to the smell in the water tank."

Descending into the basement, the damp air reeked of mildew. Yang Lin's inspection light swept across the pipe supports and spotted an anomaly: a patch of rust had been rubbed away, revealing a silvery-white metallic base. "There's a horizontal scratch here, about 30 centimeters long," he measured the scratch's height, "1.5 meters from the ground, which is consistent with the height an adult would reach when lifting heavy objects." Fiber analysis at the scratch revealed it to be blue polyester, identical to what had been found previously.

"How do you think the suspect got the body into the water tank?" Yang Sen leaned against the water pipe to rest, the beam of his footprint lamp flickering in the darkness. "The water tank's access opening is only 60 centimeters in diameter, making it difficult for an adult to pass through, unless they killed the person first and then stuffed them in." Yang Lin shook his head, pointing to the scratches on the outside of the water tank: "The scratches are going from bottom to top, more like the marks left by a living person climbing, and there are scratch marks on the inside of the tank wall, indicating that the deceased was still active inside the water tank."

A new discovery was made in the basement drain. Yang Sen's footprint lamp illuminated a silver button, round with four holes, exactly the same as the one found in the flower bushes. "There's a blue fiber wrapped around the buttonhole," he observed under the microscope, "with signs of pulling, it must have been torn from clothing." In the silt at the edge of the drain, there was also half a wrench, the same model as the one Zhou Qiang had lost, and the fingerprints on the wrench matched the unfamiliar fingerprints on the water tank lock.

“This wrench may have been left behind by the suspect,” Yang Lin said, carefully putting it away in an evidence bag. “But it only has the fingerprints of the maintenance crew and blurry glove prints on it, without any direct indication.” He squatted down beside the drainage ditch to observe. “The water flow is from the water tank to the municipal pipe network. The suspect may have wanted to dispose of the evidence here, but he didn’t do it properly.”

When the search extended to the community's green belt, Yang Sen discovered new footprints under the ginkgo trees. "These footprints are different from the previous size 44," he compared the patterns of the two. "This one has a wavy pattern, while the previous one had a serrated pattern. It must have been left by someone else. The stride length is 65 centimeters, the stride width is 18 centimeters, which gives an estimated height of 165-170 centimeters." Next to the footprints was a flattened cigarette box, also a Yuxi brand, but with a production date a month earlier than the previous one.

"Could there be accomplices?" Yang Sen speculated, but Yang Lin pointed to the fingerprints on the cigarette pack. "The DNA matches the saliva stains on the cigarette butts from before, so it should be left by the same person. They might have changed shoes." He suddenly noticed that the soil at the tree roots had been disturbed. After digging it up, he found a pit about 20 centimeters deep with a blood-stained rag buried inside. "The fabric fibers match those that blocked the overflow pipe, and the bloodstains on it tested positive for benzidine."

The two men analyzed the pit. Yang Sen used a probe to clear away the soil: "The suspect handled bloody items here, possibly tools or clothing used in the crime. This rag is very absorbent, perfect for wiping away bloodstains." Yang Lin, however, stared at the footprints on the edge of the pit: "It's a size 44 serrated shoe print, which means the suspect buried it alone, without accomplices."

During the investigation of the underground pipeline entrance, fresh pry marks were found on the edge of the metal manhole cover. "The suspect opened the manhole cover," Yang Lin said, using a laser rangefinder to measure the depth of the well. "It's 3 meters deep and connects to the community's water supply network." There were fresh footprints on the ladder below the well. "A size 44 shoe print; the red soil on the sole matches that around the water tank. He probably wanted to enter the water tank area through the pipeline but ultimately gave up." (End of Chapter)