USA Today and other media said on Monday that Armstrong confessed to doping in an interview with Oprah Winfrey to be aired later this week, and the talk show host confirmed the reports on Tuesday on "CBS This Morning."
The US Justice Department, which abandoned a two-year criminal probe into Armstrong last year without bringing charges, could decide to take a fresh look after any admission, though experts deemed that unlikely.
But several civil lawsuits, including a federal whistleblower case filed by former team-mate Floyd Landis, would be bolstered by the Texan's admission, they said.
"On one side of the ledger are the legal consequences and the financial exposure, and on the other side are the public relations consequences," said Geoffrey Rapp, a law professor at the University of Toledo in Ohio. "I think he's made the decision that the value of his name, and salvaging something from that, exceeds the legal costs."
Armstrong was stripped of his Tour de France titles and banned from cycling after the US anti-doping agency, USADA, issued a damning report in October detailing reams of evidence that Armstrong had masterminded a sophisticated doping ring for himself and his team-mates.
His sponsors, including Nike and Anheuser-Busch, which had stood by him through years of accusations that he steadfastly denied, began deserting him soon after the USADA report.
Unlike other sports stars who have been prosecuted in connection with doping, such as track star Marion Jones and baseball slugger Barry Bonds, Armstrong seems to be safe from perjury or false statement charges, according to legal experts.
His last recorded testimony under oath that he did not use performance enhancers appears to be in a 2005 arbitration case involving a dispute over whether he should receive bonus money in light of doping allegations. The statute of limitations for perjury has expired.
It is not known whether he spoke to federal investigators during their probe.
"Without knowing the details of the interview, it is difficult to read the tea leaves regarding the implications of his admissions," said Matthew Rosengart, a former federal prosecutor. "But it is reasonable to assume that the exposure would likely fall within the civil rather than in the criminal arena."
Andrew Stoltmann, a Chicago lawyer who has represented professional athletes, said if Armstrong confessed, he was running the risk that the government might reconsider a criminal fraud case.
"Why poke the bear?" he said.
Armstrong faces a number of civil claims in addition to the Landis whistleblower case, which accuses Armstrong of defrauding the government by accepting tens of millions of dollars in sponsorship money from the US Postal Service.
The Sunday Times has sued Armstrong over approximately $500,000 it paid him to settle a libel lawsuit stemming from a story accusing him of doping. A Dallas-based company, SCA Promotions, has threatened to sue him to claw back $7.5 million it paid him in bonuses for his Tour de France wins.
In both of those cases, experts said, Armstrong's admission would make it harder to mount a defence.
The biggest danger lies with the whistleblower case, said Matt Orwig, a former federal prosecutor. The False Claims Act, under which the suit was filed, allows whistleblowers to sue on behalf of the government for a percentage of the recovered funds.
Such cases typically gain momentum if the government joins as a plaintiff, a move several media outlets reported is growing likely, and the damages can be tripled under the law. If Armstrong's admission prompts the Justice Department to step in, he would face a steep uphill battle, Orwig said.
"The difference between a case in which the government intervenes and one in which they don't is enormous," he said.
"It's a whole different ballgame."
One legal issue unlikely to affect Armstrong is lawsuits filed by angry sponsors to recover money they paid him, Rapp said. While most contracts have morality clauses, sponsors rarely if ever sue athletes for damages; disgraced stars like golfer Tiger Woods haven't faced such claims, for instance.
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