I saw Jones inject herself with drugs

For just over a year, the man at the centre of international sport's biggest drugs scandal has maintained his silence. But today, in two explosive interviews, Victor Conte has made allegations that could destroy the career of one the world's most famous athletes.

Conte, head of the Balco laboratory in San Francisco which supplied illegal performance enhancing drugs to disgraced British sprinter Dwain Chambers, tells ABC television's "20/20" programme that he watched as America's Olympic triple gold medallist Marion Jones injected herself with human growth hormone.

In the 20/20 interview to be aired tonight, Conte claims he started supplying Jones with drugs in the weeks leading up to the Sydney Olympics in 2000 when she won three gold and two bronze medals. He also gave her a steroid called " the clear" which was designed to avoid detection by drugs tests.

He also says he supplied steroids to Greg Anderson, personal trainer to Barry Bonds of the San Francisco Giants who is one of baseball'sbiggest stars. Alarminglyin a separate interview published today by ESPN magazine Conte reveals he has developed a new drug which he calls "clear III" which is in current circulation.

This is the first time that Conte has spoken out since the scandal surrounding his Balco (Bay Area Laboratory Co-Operative) business broke last year.

Conte is one of four men who have formerly pleaded not guilty to charges of illegal steroid distribution in the United States.

The others are Anderson, Balco vice-president James Valente, and track coach Remi Korchemny.

In February Chambers, the European 100m champion who was a member of Korchemny's training team, was suspended for two years and banned from the Olympics for life after testing positive for the designer steroid THG.

Conte's allegations, made to "20/20" reporter Martin Bashir who gained fame for his interviews with Diane Princess of Wales and pop star Michael Jackson, come at the same time as sport in America has been rocked by leaked reports from a Grand Jury investigation into the Balco affair.

Bonds, the holder of baseball's single-season home run record of 73 in 2001 and the man who is on course to break Hank Aaron's all-time career home run record of 755, is reported to have testified that he did use a clear substance and a cream given to him by Anderson without knowing they were steroids.

Jason Giambi, of the New York Yankees, is also said to have told the Grand Jury in a secret session that he injected himself with human growth hormone and used steroids for at least three seasons.

That revelation, which appeared in yesterday's San Francisco Chronicle, could cost Giambi his contract with the Yankees worth nearly £70 million.

Lawyers for Jones, who has never failed a drugs test, have moved quickly to deny Conte's allegations.

Her attorney, Richard Nichols, said: "We invite the public to decide: Victor Conte is a man facing a 42-count federal indictment while Marion Jones is one of America's most decorated female athletes.

"Mr Conte's statements have been wildly contradictory, while Marion Jones has steadfastly maintained her position throughout: she has never, ever used performance enhancing drugs."

"Mr Conte chose to make unsubstantiated allegations on television, while Marion Jones demanded to take and then passed a lie detector examination. Mr Conte is simply not credible.

"We challenge him to submit to the same lie detector procedure that Marion passed."