Tyler Hamilton's lawyers on Monday formally notified federal authorities about a weekend incident they consider to be "aggressive contact" initiated by Lance Armstrong, saying it is up to those authorities to decide whether it constitutes witness tampering.

Hamilton, 40, who testified behind closed doors before a federal grand jury hearing evidence against Armstrong and others last summer, made specific doping allegations against the seven-time Tour de France winner on CBS' "60 Minutes" last month.

The two cyclists crossed paths at an Aspen, Colo., restaurant Saturday night, said Hamilton attorney Chris Manderson. He said Hamilton told him Armstrong repeatedly asked how much he had been paid to do the television interview, and added that his legal team would "(expletive) destroy you," "tear you apart on the witness stand," and "make your life a living (expletive) hell."

Tyler Hamilton, left, has admitted to doping and said he observed one-time teammate Lance Armstrong cheating, as well. Damien Meyer/AFP/Getty Images

Manderson said Hamilton was unnerved by the episode. The lawyer said he felt compelled to inform federal authorities of the incident.

"Lance Armstrong is a possible defendant in an investigation that's been widely reported, and Tyler is a probable witness," Manderson said. "When there's any contact, especially aggressive contact, we as lawyers have a duty to inform the authorities. ... What they will do with it, I don't know."

Jodi Larner, co-owner of the upscale Cache Cache bistro where the incident took place and a personal friend of Armstrong's, told a diametrically opposed version of events. She said she was standing close to Armstrong when Hamilton walked by. Larner said she did not overhear the entire conversation, which she characterized as brief.

But based on the body language of the two men and what she did hear, she said, "It was not combative. It was not hostile ... There were no threats. There were very few words exchanged. There was no scene made."

"Lance never left the barstool," Larner added. "It was like two dudes meeting serendipitously. It was not a big confrontation." She said the men's voices were not raised and called what she had read of Hamilton's version "fictitious."

Larner said the FBI was coming Wednesday to take the restaurant's surveillance tapes. However, the tapes only capture the kitchen area and not the front of the restaurant where the incident occurred.

"I wish it was on surveillance to show it was a non-event," said Larner, a friend of Armstrong's. "... "They didn't create a scene whatsoever. Two guys talking in a bar. If that's an incident, wow."

Armstrong's spokesman, lawyer Mark Fabiani, declined comment Monday but on Tuesday told The Associated Press that the meeting was a nonevent, and offered up a list of witnesses to back up his claim. Armstrong himself downplayed the incident, calling it "certainly awkward for both of us" and "truly uneventful" in comments reported by Outside Magazine writer Abe Streep, who posted a blog entry after riding with Hamilton on Sunday.

The 39-year-old Armstrong lives part-time in Aspen with his girlfriend and mother of his two youngest children, Anna Hansen. Hamilton, a Boulder resident, was in Aspen last weekend to speak and lead rides at an event sponsored by Outside Magazine that featured a number of athletes from adventure sports. The event, Hamilton's first public appearance since the "60 Minutes" segment aired, was promoted nationally.

On Saturday night, Hamilton went to dinner with friends at Cache Cache, unaware that Armstrong is a frequent patron there, Manderson said. Hamilton told Manderson he was walking through the crowded bar area on his way back from the men's room when he spotted a woman he knew and approached her, only to feel Armstrong's hand on his chest stopping him.

The two men greeted each other awkwardly. Hamilton told Manderson that Armstrong sarcastically asked him how he was. The startled Hamilton then said he was sorry for everything that had happened, prompting Armstrong's derisive comments.

Hamilton told his lawyers he did his best to stay composed, told Armstrong he had not been paid anything by CBS, and asked Armstrong several times to continue the discussion in private or at least away from the bar crowd. He said Armstrong refused and continued to castigate him.

After a few minutes, Hamilton told Manderson that he returned to his friends at the table, where the waiter who had taken their order made it clear he was no longer welcome. They finished their coffee and dessert and left. Larner said she spoke to Hamilton on his way out and asked him never to come back because people at his table had been rude to her staff and failed to tip. (Hamilton told Manderson there was a "misunderstanding" about the bill that was resolved before he and his friends left.)

California-based former federal prosecutor Richard J. Cutler has no first-hand knowledge of the incident but said that the episode, if accurately recounted by Hamilton, could fall within the definition of witness tampering.

Although no criminal charges have been filed against Armstrong, Cutler said the ongoing investigation could be enough to underlie a charge of witness tampering. Hamilton could be called back before the grand jury to provide more information, and/or summoned to testify at trial if a case were to go that far.

"If I were the prosecutor, my investigator would be going to talk to Hamilton," said Cutler, now with the firm of Dechert LLP. "This, to me, is a game-changer."

A charge of witness tampering could also affect any statute of limitations issues prosecutors might be facing by extending the timeline forward to the present day, Cutler added.

The main focus of the investigation is the years 1999-2004, when Armstrong rode for the U.S. Postal Service team. Authorities are considering whether evidence supports possible charges of fraud and conspiracy in relation to use of sponsorship funds for alleged organized doping.

Armstrong continues to deny ever having used performance-enhancing drugs. His attorneys demanded an apology from "60 Minutes" after Hamilton's interview aired, but CBS stood by the story.

Bonnie D. Ford covers Olympic sports and tennis for ESPN.com. Information from The Associated Press was used in this report.