Zhang Jinfeng, who worked with Zhang Yan for 13 years, said the late officer regarded criminal investigation as his lifelong work.

"We learned a lot about investigation and interrogation techniques from him, and he was a role model for us," he said.

Zhang Yan's wife Gao Yun said he always gave priority to his job.

Due to his work he missed their wedding ceremony in 1994 and their daughter's birth the next year, Gao said.

When his mother died in 2003, Zhang was chasing a group of suspects in another province and arrived home five days after she passed away.

Born in 1969, Zhang Yan joined the Qinhuangdao public security bureau in Hebei Province in 1990 after graduating from the Criminal Investigation Police University of China, in Shenyang.

During the national campaign launched by the central government in 2018, he commanded and participated in the investigation of 16 mafia-style organizations and 65 other criminal gangs, the bureau said.

Zhang also promoted training of police officers to adapt to emerging crimes.

He was involved in the building of the first center in Hebei province to deal with telecom fraud and the formation of teams in 2016 to fight such crimes.