Los Angeles (CNN) -- It is unlikely that Lance Armstrong will face criminal fraud or perjury charges in connection with a closed federal investigation despite his admission of using banned performance-enhancing drugs, a source with knowledge of the probe told CNN Friday.
The investigation was closed last February without any charges against the now-dethroned seven-time Tour de France champion. Although he has admitted that he lied about his use of banned substances and procedures, he wouldn't face perjury charges in connection with the probe because he never testified in the proceedings, the source said.
The source confirmed that investigators focused their probe on allegations of potential fraud, based on the activity of a racing team partly owned by Lance Armstrong that received a sponsorship contract from the U.S. Postal Service between 1998 and 2004.
Despite Armstrong's statements, the statute of limitations on a criminal fraud scheme is five years, which could pose problems should the government consider reopening the case. Armstrong told Oprah Winfrey he stopped doping following his retirement in 2005.
The Justice Department had no comment on whether it might reopen the criminal investigation in light of Armstrong's comments to Oprah.
The nearly two-year inquiry, centered in Los Angeles, involved evidence gathered by federal prosecutors that including sworn testimony from Armstrong's former teammates, associates and friends. According to the source, the probe began with a separate investigation of a California racing team in 2008 whose members included former teammates of Armstrong. The source would not identify the team.
According to the source, the criminal probe accelerated when former cycling champion Floyd Landis, one of Armstrong's former teammates, went public in 2010 alleging he and other top riders, including Armstrong, had engaged in widespread doping while on the Postal Service team.
According to the source, prosecutors examined whether a doping program was developed for Armstrong's team during the period when it received millions of sponsorship dollars from the U.S. Postal Service. The criminal probe was focused on whether Armstrong engaged in criminal fraud through "financial transactions" if the government could prove he violated anti-doping clauses in his contract with the Postal Service, the source said.
The source added that investigators probed "what kind of alleged doping occurred and how it occurred."
On February 3, 2012, U.S. Attorney Andre Birotte Jr., representing the Central District of California, announced that his office was closing the investigation into "allegations of federal criminal conduct by members and associates of a professional bicycle racing team owned in part by Lance Armstrong."
In Birotte's statement announcing the decision, he commended the joint investigative efforts of his prosecutors and special agents, including "the U.S. Food and Drug Administration, the Federal Bureau of Investigation and the United States Postal Service Office of the Inspector General." He gave no reason for closing its investigation.
Loyola Law School professor Laurie Levenson, a former federal prosecutor in Los Angeles who watched Winfrey's interview and followed the criminal probe, said the timing of Armstrong's admitted doping must have played a role in his decision to confess.
"Nothing he said would likely subject him to further criminal charges because the statutes expired, and he did not say how it happened nor did he implicate others in a way that would constitute a general scheme to defraud the federal government," Levenson said. "In terms of transparency, Armstrong's interview was a mixed bag, and I'm sure his answers were part of a carefully crafted strategy to avoid criminal liability."
An attorney representing Armstrong in the criminal investigation did not respond to repeated phone calls for comment.
According to the source, the purpose of the probe was not to build a case on whether Armstrong or his teammates used banned substances, but rather to establish evidence beyond a reasonable doubt that Armstrong violated criminal fraud statutes.
The credibility of Landis and other cycling team members also posed problems for the government's case, given their previous denials of using banned substances, the source said.
When the case closed without further action, Armstrong issued a statement on his website. "I am gratified to learn that the U.S. attorney's office is closing its investigation," Armstrong said. "It is the right decision and I commend them for reaching it. I look forward to continuing my life as a father, a competitor, and an advocate in the fight against cancer without this distraction."
Unlike the Barry Bonds and Roger Clemens case, in which both baseball stars testified before a federal grand jury and Congress and were accused of lying under oath, Armstrong was not questioned by federal authorities under oath, and therefore was not exposed to potential criminal perjury charges in the Los Angeles case, the source said.
When asked by Winfrey about the Department of Justice decision to drop the case, Armstrong said, "I thought I was out of the woods. And those were some serious wolves."