"It's like a hunt, full of wisdom and challenge. We rush about at intricate crime scenes, letting the evidence speak and the truth be heard."

The 2024 Spring Festival travel rush came to an end on March 5. Among this "super passenger flow" expected to exceed 8.4 billion cross-regional trips, there is a group of "invisible warriors" who, relying on professional knowledge and advanced technology, decipher the "silent codes" from the slightest traces, quietly guarding the "safe journeys" of countless travelers.

Zhao Kun, 40, is a police officer of the Criminal Technology Detachment of the Tianjin Public Security Division of the Beijing Railway Public Security Bureau, and also a professional engineer in trace examination. Compared with other posts in the railway public security departments, Zhao Kun's work is professional and mysterious; although there are no thrilling scenes of arrests or fighting crime, he can make the clues at crime scenes "speak."

"Every crime scene is a puzzle the suspect sets for us. What we need to do is track down the trail like a hunter—fast, steady, and accurate! So that criminals have nowhere to hide." In Zhao Kun's view, no matter how cunning a suspect is, they will leave more or less traces at the scene. Although cracking the case may often be like "looking for a needle in a haystack," not the slightest carelessness is allowed, "because any negligence may be conniving at crime."

Zhao Kun told reporters that once, a theft occurred on an abandoned railway line within the jurisdiction of the Tianjin Railway Public Security Division, where the suspect used a rail-cutting machine to steal and cut more than ten meters of steel rail. It was the depths of winter, and the water droplets on the wires had frozen into ice. When he and his colleagues arrived at the scene to investigate and measure, their hands and feet had gone numb from the cold, and their jaws were shivering uncontrollably.

From the central scene, the entry and exit routes, and the peripheral scene in different areas, Zhao Kun squatted on the ground, examining bit by bit and collecting bit by bit, carrying out a "carpet-style" search with his colleagues. By the time he returned to the detachment, it was already midnight. Regardless of rest or food, he processed the pieces of physical evidence extracted one by one overnight, and after processing, classified and sent them to the physical evidence appraisal center.

After appraisal, traces of a suspect were found in the submitted physical evidence; this person had been dealt with by public security organs in 2014 for a theft case. Thus, the suspect in the steel rail theft-and-cutting case was successfully identified, and it took only 42 hours from the occurrence of the case to the identification of the suspect.

Long-term criminal technology work has given Zhao Kun both meticulousness and keenness in investigative awareness, and has also honed a pair of "piercing eyes." Over more than ten years, he has participated in the investigation of more than 600 scenes of various cases and incidents. Not a single hair, a drop of blood, a fingerprint, or a shoe print can escape his " forensic eye."

Once, a theft occurred in a dormitory of the Chentangzhuang freight yard under the jurisdiction of the Tianjin West Railway Station Police Station. There was no surveillance equipment at the crime scene, and after the incident, the victim and other personnel entered the scene several times in succession, causing great difficulties for on-site investigation and the search for physical evidence.

By questioning the victim and his roommates, Zhao Kun, relying on his solid professional competence, reconstructed the original state of the scene and used technical means to simulate the suspect's movement trajectory.

During the investigation, Zhao Kun extracted a not-so-obvious shoe print. The location of the shoe print was unusually strange, and it did not appear to have been left by the victim or his roommates. After comparing the shoe prints of all personnel at the scene one by one, he inferred that this was very likely the shoe print left by the suspect.

Based on this information, the investigators quickly identified the suspect and brought him to justice. On the day of the arrest, Zhao Kun rushed to the detention center overnight, collected shoe print samples from the suspect, and conducted examination and appraisal against the shoe print samples extracted from the scene, promptly reaching a conclusion of identification, which provided strong technical support for cracking the theft case.

Zhao Kun said that on-site investigation and physical evidence extraction are dull and fraught with difficulties, requiring one to face foul odors and messy, complex environments, while often the tiniest traces may become major clues for solving a case. "Without solid and strong professional knowledge and competence, it's impossible."

On Zhao Kun's desk are thick professional books as well as tools such as chemical reagents. Having loved criminal investigation and case-solving stories since childhood, he is still almost "obsessed" with his passion for this profession today. "Criminals' methods are constantly being updated. As a trace examination officer, if you are not prepared and cannot cope with one 'new' situation after another, you will be eliminated!"

In Zhao Kun's view, this profession is like a case-solving "navigation device" on the railway. They must keep their eyes fixed on the front line of criminal technology and provide as accurate case-solving information as possible, while on their shoulders rests a responsibility "as heavy as a thousand catties."

"On the tens of thousands of miles of railway lines are the 'mobile homes' of millions of travelers. Likewise, millions of staff members are quietly guarding this 'home.'" Zhao Kun said that although the Spring Festival travel rush has ended, they will always be on the road to "home," traveling day and night.