The Canadian man who was sentenced in Vietnam to four years in jail for abusing teenage boys was caught with the help of an Australian charity that located his victims and tipped off police.

Vadim Scott Benderman, 45, formerly of Montreal, admitted during his half-day trial on Wednesday that he lured four boys into his home in Hanoi and paid them between $10 and $15 to have sex, according to a Hanoi court official who spoke on condition of anonymity.

A judge sentenced Benderman to four years in prison and ordered he be expelled from the country after serving his sentence, the official said.

Michael Brosowski, founder of the Blue Dragon Children's Foundation, which helps homeless and trafficked minors in Vietnam, said Benderman's arrest was partly the result of investigations by his staff.

In an interview with The Canadian Press from Hanoi, Brosowski said his charity has a program to help street children.

During a routine visit to lakes and parks where homeless kids congregate at night in the capital, he said his staff met with Benderman's victims.

"Since 2013 we have been finding that a majority of the children we meet on the streets -- most of whom are boys -- have been approached by pedophiles," he said. "And sadly many have already gone with the pedophiles by the time we meet them."

Brosowski said in 2014 several boys told his foundation's social workers they had been abused by a foreigner whom they called Ben or Dan.

A few months later another boy told Brosowski's staff he had recently been with the same man and disclosed his home address and his Facebook profile, which was under the name Dean Wilson.

"We continued receiving information from the children and watching out for the man in our street outreach work," Brosowski said. "The breakthrough came when we discovered his email address, which through an online search revealed his real name. We could see he had previously been arrested in Cambodia."

Brosowski said based on the info they collected, Hanoi police were able to set up a sting and catch Benderman with an underage boy.

The Blue Dragon organization is an Australian charity based in Hanoi and was started by Brosowski in 2003.

He said his charity provided a lawyer, Van Ta, who represented the four boys, who were between 13 and 15 years old.

Benderman was officially charged with obscenity against four children, Brosowski said, adding Benderman has 15 days to appeal the verdict.

"Normally in a case like this the convicted person would pay compensation to the victims," Brosowski said. "(Benderman) argued that he had no money so he didn't have to pay."

The Hanoi court official said Benderman admitted that he abused each boy from one to three times over a period of several months until his arrest last June.

"The defendant's crime was very serious for society," the official quoted the verdict as saying. "It infringed upon the normal development of the boys."

Child sexual abuse carries a penalty of three to seven years in jail. Benderman was given less than the maximum sentence because of his sincere confession, the official said.

It is unclear when Benderman arrived in Vietnam.

Hanoi media reported he arrived in the country in June 2014 on a tourist visa. Other media reported he taught at a Cleverlearn English Language Centre in Hanoi.

A spokesman for Global Affairs Canada said the department was aware of a Canadian citizen "detained and facing legal proceedings in Vietnam" but wouldn't confirm any information about the person's identity.

Brosowski said Vietnam is currently in the process of reforming its child abuse laws to make them "clearer and stronger."

He said "with the legal reform process taking place we expect that the authorities will soon be able to investigate and press charges more easily in such cases."

With files from The Associated Press