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

“The stride was about 60 centimeters, the gait was very steady, and there were no signs of dragging heavy objects.” Yang Lin carefully measured with a ruler. “The suspect should be about 175 centimeters tall, of medium build, and very calm when committing the crime.”

Yang Sen took out red footprint fixative from the investigation kit and sprayed it evenly on the footprints. "These footprints are much clearer than the ones next to the body. The pile of debris blocked the airflow, so the dust wasn't blown away." He squatted down to observe the details of the footprints. "Look here, there's a small notch at the toe of the shoe, probably caused by wear on the sole. This is an important feature." The fixative slowly solidified, and the two used a transparent plastic film to carefully extract the footprints and place them into an evidence bag.

After clearing the top of the pile of debris, Yang Sen climbed down the ladder, his gaze falling on the broken window on the east side. Fresh sawdust still clung to the edges of the pried-open plank. He used tweezers to pick up the sawdust and put it into an evidence bag, then shone his investigation light on the wall inside the window. The wall was riddled with cracks, and under the beam of light, a tiny scratch stood out. "This wasn't formed naturally," Yang Sen said, gesturing with his finger to indicate the length of the scratch. "About 10 centimeters, with clean edges, like it was scraped by a metal tool."

Yang Lin leaned closer, took out a multispectral lamp from the investigation kit, and swept the purple beam across the scratch, immediately revealing a few faint reflections on the wall. "There's metal residue," he said excitedly, gently wiping the scratch with a cotton swab dipped in a special reagent. The swab instantly turned a light gray. "It should be left by a tool like a crowbar. We'll do a composition analysis when we get back, maybe we can pinpoint the type of tool."

The two carefully examined the wall, and on the ground below the window, Yang Sen suddenly discovered a cigarette butt half-covered in dust. "'Double Happiness' brand, the same brand as the cigarette butt next to the body." He used tweezers to pick up the cigarette butt and put it into a sealed evidence bag. "The cigarette butt is still intact, and there are obvious teeth marks on the filter, indicating that the smoker is used to biting the filter with his teeth, which is also a personal characteristic."

"Do you think the suspect might have smoked while keeping watch by the window?" Yang Lin asked. He walked to the window, pushed aside the pried-open wooden board, and saw the back wall of the dormitory building outside. The base of the wall was overgrown with weeds, and in the distance was a wasteland. "You can see the main road of the factory from here. If there are security guards patrolling, they can spot you at a glance."

“Very likely.” Yang Sen nodded. “He pried open the window to come in, observed the surroundings from the window first, and only acted after confirming it was safe. After committing the crime, he left through the front door, which was both concealed and not easily discovered.” He squatted down and used an electrostatic adsorbent on the ground around the window. Several thin, dark blue fibers quickly adhered to the adsorption film. “These are not fibers from old clothes in the attic. The fibers of old clothes are faded and yellowed, but this color is very bright.”

Yang Lin took the absorbent membrane and examined it carefully against the light: "It looks like new workwear fibers. The workwear issued by the fertilizer plant this year is this color." He suddenly remembered something, "Wang Shuai said Li Dahai's work clothes are dark blue. Could it be related to him?"

“It’s hard to say. This kind of fiber is too common. Most of the workers in the factory have it.” Yang Sen put away the absorbent membrane. “We’ll go back and do a composition comparison to see if it’s the same as the fiber in the clothes Li Dahai lives in.”

The investigation continued until 6 p.m., the last rays of the setting sun streaming through the broken window into the attic, casting long shadows of the two men. Besides footprints, scratches, cigarette butts, and fibers, they also found a faint fingerprint tucked into a crevices of a pile of debris, imprinted on a broken enamel mug. "Only some of the fingerprint's lines are clear; there aren't enough distinguishing features to make a direct comparison right now," Yang Sen said regretfully. "But we can enter it into the database first and investigate further."

The two carefully packed all the collected evidence into their investigation kit, preparing to return to the Criminal Investigation Division. As they left the attic, Yang Sen glanced back at the location of the body covered by the canvas. "Old Yang, who do you think the deceased was? Why was he in this abandoned attic?" "Judging from the old employee badge in his pocket, he's definitely connected to the fertilizer factory," Yang Lin said, locking the attic door and sealing it. "He could be a former employee, or he could be looking for someone. Either way, we have more leads now. If we can connect them, we'll find a breakthrough."

Back at the Criminal Investigation Division, Yang Lin and Yang Sen immediately sent the physical evidence to the Technical Section. In the laboratory, they watched with anticipation as technicians conducted preliminary tests on the cigarette butts, fibers, and metal residue. "Complete DNA was extracted from the cigarette butts and is being compared with the database; the fibers are a cotton-linen blend, consistent with the composition of work clothes from fertilizer plants; the metal residue is preliminarily identified as carbon steel, commonly found in ordinary crowbars," the head of the Technical Section reported the preliminary results.

"What about the fingerprints? Have you found the results?" Yang Sen asked anxiously.

"Not at the moment." The head of the technical department shook his head. "There are too few fingerprint feature points, and there is no matching information in the database. We are currently performing image enhancement processing, hoping to extract more feature points."

At 9 p.m., the DNA comparison results came back—the DNA on the cigarette butt did not belong to Li Dahai or Zhang Jianguo, nor was it in the database of criminal records. The fiber composition comparison results showed that it was the same as the fiber composition of the work clothes at Li Dahai's residence, but the technicians explained: "This kind of fiber is very common in fertilizer plants, and we cannot conclude that it is related to Li Dahai just because the composition is the same."

Yang Lin and Yang Sen sat in the technical department chairs, their brows furrowed. Although expanding the investigation area had yielded numerous clues, these clues were scattered and did not form a complete chain. Footprints could determine the suspect's height and build, cigarette butts could provide DNA, and fiber and metal residue could narrow down the range of tools and clothing, but none of these were enough to identify the suspect. The identity of the deceased was even more uncertain; the name on the old work badge was worn away and illegible, and DNA comparison did not yield any missing persons information.

“Don’t worry, we’ve made a lot more progress than this morning.” Yang Lin patted Yang Sen on the shoulder. “At least we know that the suspect is a male who wears size 42 shoes, smokes ‘Double Happiness’ cigarettes, and may be wearing dark blue work clothes. These are all important pieces of evidence for our investigation.”

“Let’s go to the attic again tomorrow and see if we can find any more clues.” Yang Sen stood up. “There might be places we’ve missed, like the pockets of those old clothes or the hidden compartments in the wooden box.”

At this moment, Wang Shuai returned from his outreach, bringing new information: "I asked some veteran employees of the fertilizer plant today, and they said that ten years ago, an operator named Zhao Jianjun left the company and disappeared without a trace. He was about the same age as the deceased, but nobody knows where he is now." (End of Chapter)