Lance Armstrong, the disgraced Tour de France cyclist, is facing fresh claims that he lied over his drugs-cheating - this time in his confession to Oprah Winfrey that he doped.
The chief executive of the American anti-doping authority has written to Armstrong to say that he failed to confess the full extent of his cheating to Winfrey, and specifically lied when he claimed to have raced "clean" in 2009.
But Travis Tygart has also told the cyclist, who has been stripped of his seven Tour de France victories, that it could be possible to reduce the lifetime ban from competitive sport he is currently serving in return for a full confession to the authority setting out who helped him cheat and how.
The extraordinary offer suggests that it is possible that one of Armstrong's key aims in finally offering a confession to Winfrey - being able to compete in sport again in the future - could be achieved.
However Mr Tygart, who leads the United Stated Anti-Doping Agency (USADA), said the offer would end on February 6, and hinted that criminal action could follow afterwards.
The most damaging consequence Armstrong could face is prosecution for perjury, having signed sworn statements to American federal authorities that he was not a drugs cheat.
Mr Tygart said that when Armstrong confessed to Winfrey that he had been a drugs cheat for all seven of his Tour de France titles he was telling the truth.
However Armstrong, 42, was adamant that his comeback in the 2009-2010 cycling season had involved no drugs.
This, Mr Tygart said, was both untrue and an attempt to avoid criminal action as he could be prosecuted for criminal fraud over misleading his sponsors that he was clean. The earlier years would be covered by the American statue of limitations on fraud, which prevents cases being resurrected years after the offences were committed.
Mr Tygart told the American broadcaster CBS's 60 Minutes documentary programme that the claims of a clean comeback were "just contrary to the evidence".
"His blood tests in 2009, 2010 - expert reports based on the variation of his blood values - from those tests, one to a million chance that it was due to something other than doping," he said.
Mr Tygart said there was solid evidence of cheating because there was correspondence between Armstrong and Dr Michele Ferrari, who has been banned from helping athletes for life over his involvement in doping, during his comeback season.
Armstrong would have no reasons to be in touch with the doctor other than doping.
The USADA chief executive also warned of other misleading claims made by Armstrong in his interview.
He said that the cyclist had claimed to use only small amounts of the blood "booster" EPO, which increases athletes' endurance.
"He used a lot of EPO," Mr Tygart said.
"You look at the '99 Tour de France samples and they were flaming positive, the highest that we've ever seen. And he's now acknowledged those were positive."
Armstrong also denied offering USADA a donation of $250,000, which Mr Tygart had disclosed earlier this month.
In the CBS interview, Mr Tygart said he stood by his allegation and said: "It's one of his closest representatives. I've told the federal government in its investigation on the civil fraud side, so I don't think it would be appropriate now to name the name because it's still one of his closest representatives."
The cyclist's claim that he did not intimidate his team into cheating was also rubbished by the anti-doping official.
"He was the boss," he said.
"The evidence is clear he was one of the ringleaders of this conspiracy that pulled off this grand heist that defrauded using tens of millions of taxpayer dollars, defrauded millions of sports fans and his fellow competitors."
His reference to American pubic money being spent is because Armstrong was sponsored by the United States Postal Service, before being sponsored by the Discovery Channel.
And Mr Tygart reacted angrily to Armstrong saying that he did not consider himself a cheat because he had looked the word up in the dictionary and seen that it was defined as seeking unfair advantage. The cyclist said he was simply levelling the playing field because all other cyclists were cheating.
Mr Tygart said: "It's amazing. You could go to almost any kindergarten in this country or frankly around the world and find kids playing tag or four square and ask them what cheating is.
"Every one of them will tell you it's breaking the rules of the game. No real athlete has to look up the definition of cheating. And it's offensive to clean athletes who are out there working hard to play by the rules that apply to their sport."
He added: "It's just simply not true. The access they had to inside information, how to test, what tests were in place and what time. He was the one on an entirely different playing field to other athletes, even if you assume other athletes had access to some doping products."