In the meticulous world of forensic science, a single fingerprint can speak for a victim who can no longer find their voice. But last July, one of the most respected voices in Chinese forensics fell silent.

Zhang Xuejie, a man who spent 33 years finding the truth in the smallest fragments of a crime scene, died suddenly in the line of duty at the age of 55. He was struck by illness following a period of high-intensity work — a final act of dedication to a career defined by the pursuit of "zero mistakes".

Posthumously honored as an outstanding Communist Party of China member of Zhuhai, Zhang leaves behind a legacy that isn't just written in awards, but in the 800 solved cases that might have otherwise gone cold. To his colleagues, he wasn't just an expert; he was the "final line of defense" for justice.

When Zhang joined the police force in 1992, Zhuhai, in South China's Guangdong province, was a rapidly transforming frontier. While many of his peers sought the spotlight of frontline investigation, Zhang chose the shadows of the lab.

Whether a case can be solved depends on the evidence. Whether justice can be upheld depends on technology, Zhang would say.

In the 1990s, forensic work in Zhuhai was in the development stages. Equipment was basic, staffing was limited and professional standards were still being built. Without advanced instruments, officers relied on direct observation, manual comparison and repeated examinations. They learned through practice and improved through real cases.

By day, Zhang followed senior colleagues to crime scenes, learning how to search, collect and preserve evidence. At night, he studied trace examination, forensic photography and other technical subjects, filling notebook after notebook with detailed observations. When he encountered difficult questions, he sought out experts and reviewed case files to find answers.

He understood that forensic science allowed no carelessness and no falsehood. A fingerprint, a fiber, a bloodstain or a set of data could change the direction of an investigation and affect a person's fate.

Over 33 years, Zhang's work took him across Zhuhai's urban districts, rural villages and islands, tracking evidence. In 2008, a baffling homicide in Zhuhai's Doumen district left investigators facing a dead end. The case stalled until Zhang, then an instructor with the fifth brigade of the criminal investigation detachment, led a team of forensic specialists back to the scene. Under his direction, they carried out a full re-examination.

In the end, Zhang found what others had missed: a partial fingerprint on the plastic seal of a water bottle — so hidden it could easily have been overlooked. The print was poor in quality, but Zhang turned it into decisive evidence that helped solve the case.

Colleagues remember Zhang as a demanding but caring mentor. Sun Junliang, a technician who worked with him, recalled the re-examination of an unnatural death case about 18 years ago. Zhang led the team back to the scene and used careful logic to reconstruct the victim's movements before death, providing a precise plan for the renewed investigation.

Seeing such professionalism up close left a lasting impression on Sun, who said that Zhang's insistence on a complete chain of evidence, and his refusal to stop before the facts were fully established, changed the way he approached forensic work for the rest of his career.

In regard to technical work, Zhang was exacting. If procedures were not standardized, they had to be redone. If results were not accurate, they had to be checked again. If reasoning was not rigorous, he would point it out directly. But in daily life, colleagues said, he treated younger staff with patience and warmth, guiding them like an older brother.

Zhang often encouraged younger colleagues with a simple belief: justice may be delayed, but it will not be absent. Every extra effort, he said, brought the truth one step closer and left the public with one less regret.

As science and technology evolved, Zhang pushed forensic work to evolve with them. As crime became smarter, more concealed, more networked and more cross-border, he said police technology had to move even faster.

Under Zhang's leadership, Zhuhai's criminal forensics team made three major transitions: from traditional manual comparison to technology-enabled work; from scattered, point-by-point efforts to more integrated operations; and from experience-based judgment to more precise, standardized, digital and law-based forensic identification.

By the time of his death, he had participated in the on-site examination of more than 2,000 criminal cases, handled over 4,000 trace evidence items, issued more than 400 forensic examination reports and assisted in solving more than 800 cases.

He also trained 14 national-level forensic talents and five provincial forensic specialists. Under his leadership, Zhuhai police laboratories in DNA, physical and chemical analysis, trace evidence and electronic evidence were recognized as key forensic labs. Over the years, Zhang received seven third-class merit citations and 12 commendations. He was named among the first group of national young talents in criminal forensic science and was twice appointed by the Ministry of Public Security as a national criminal technology specialist.

yangzekun@chinadaily.com.cn