Now 48, he has remained single just to track down whoever killed his mother, Phan Thi Khanh, in 1980. Marriage and its attendant requirements would only be a hindrance to his search, he feared, he says.

In 1976 An, then two, moved from Binh Dinh to Binh Thuan, both in south central Vietnam, to live with his mother and brother, sent by his grandmother after his grandfather died, unable to support him.

Khanh had worked and saved for years, and managed to buy 60 grams of gold. After once seeing her house burn down, she kept the gold on her person at all times.

On July 31, 1980, she went out to the field but never returned.

At around 7 p.m. her family and neighbors discovered her body by the road, the gold gone.

The local police arrested a man named Vo Te who lived close to the crime scene on suspicion he was the one who had robbed and murdered Khanh, but released him five months later for lack of evidence.

An said: "My mother died and so I lived with my uncle. Every day I had to do the housework and take care of my two cousins. My uncle beat me often. A neighbor took pity on me and took me in."

The police never found the killer. But another neighbor always used to tell him about one suspect, Truong Dinh Chi, a relative of An's uncle. The neighbor believed Chi was the one who killed An's mother.

He says: "The neighbor said that a few days before my mother was murdered, Chi and his wife came to stay at my uncle's house. Two days later they suddenly disappeared."

Life on the hunt

At the age of 12 An started his own investigation.

He worked in many different jobs in different places hoping to get information about Chi.

In 1990 he caught wind that Chi's family had moved to Hau Giang in southern Vietnam. He tracked down their address in Long Phu District and reported it to the police. But by the time the Binh Thuan police reached the place, Chi had again fled.

An did not give up and became a driver so that he would have the opportunity to travel to more places. He frequently went south, around Ho Chi Minh City and Dong Nai, Vung Tau and Soc Trang provinces.

One day he learned that Chi had changed his name to Le Minh Son and moved to Binh Dinh, and reported this to the police.

Son remained a step ahead of the police and escaped again, but did leave behind personal identification documents in the name of Le Minh Son.

He was declared wanted by the police in 1999.

A picture of Le Minh Son (L), also known as Truong Dinh Khoi and Truong Dinh Chi, along with a notice as a suspect in a robbery and murder by the Binh Thuan Province police in 1999. Photo obtained by VnExpress

A few years ago An received a tip-off from a relative that Son had changed his name to Truong Dinh Khoi and was living in HCMC. He informed the police, who acted quickly, but since he had changed his name, investigators were unable to apprehend him as they were not able to verify his identity in time and he got away.

The case was put on hold by authorities for several years until 2020 when An requested the Binh Thuan police to continue with the investigation and told them Khoi had another name, Le Minh Son, and was living in Dong Nai.

But this time too he eluded them.

In late 2021 the hunt came to an end when Chi was arrested while living in Phu Yen Province, which borders Binh Dinh.

He later admitted to killing Khanh.

But despite his confession authorities were unable to prosecute him since the limitation period had run. In Vietnam, there is a 20-year limitation period for particularly severe crimes.

On January 5 this year the Binh Thuan police suspended their investigation.

An, who believed the decision was unlawful, filed a complaint with authorities, demanding they should continue with the investigation and charge Chi for his mother's murder.

He is also seeking compensation of over VND6.5 billion ($284,588) from Chi for the emotional and mental stress he had caused.