MADRID (AFP) - As the state executioner for Virginia, Jerry Givens put to death 62 people, but after he ended up in jail himself for a crime which he says he did not commit, he has become an outspoken opponent of capital punishment.

The 60-year-old African-American worked as a correctional officer in the southern US state between 1974 and 1999 when he was charged with money laundering and perjury and was forced to resign.

"In 17 of those 25 years I executed 62 people, I executed 37 by electrocution and 25 by lethal injection," he said, his voice trembling with emotion, on the sidelines of the four-day World Congress against the Death Penalty which got underway in Madrid on Wednesday.

"It was like a rollercoaster, up and down, because as a correctional officer I prepared inmates to return into society as a productive citizen and as an executioner you take lives," added Givens, who worked first at Virginia State Penitentiary and then Greenville Correctional Centre.

As the state executioner he would shave the head of convicts facing the death penalty and then strap them into Virginia's electric chair or inject them with a lethal mix of drugs.

"We put a cap over your head and send in 3.000 volts to your body, that is gross," said Givens.

The white-bearded Givens said he would meet with convicts 15 days before they were to face the death penalty.

"I talked to them to make sure that they were ready," he said.

Givens said that at the time that he worked as an executioner he felt "that person does not deserve to live".

His view of the death penalty changed in 1999 when authorities accused him of buying a car with a friend with funds that he knew came from drug dealing and charged him with money laundering and perjury.

Givens, who maintains his innocence, was convicted and spent four years in jail.

"Then I asked myself: were some of these 62 people treated unfairly like me? I don't know that, but there is a possibility," he said.

"In my country you are subject to have an unfair trial if you don't have a lot of money," he added at a press conference at the congress, organised by the French lobby group Ensemble Contre La Peine de Mort (Together Against the Death Penalty).

About 1,500 people from 90 countries - including high-profile politicians such as French Foreign Minister Laurent Fabius, former death row inmates, human rights activists and family members of people facing execution - are expected to gather for the congress, the fifth of its kind.