Armstrong made headlines recently when he admitted during an interview with Oprah that he had used the drugs.

Now ABC News reports that a source told them "Agents are actively investigating Armstrong for obstruction, witness tampering and intimidation."

TMZ reports that multiple cyclists, as well as other people close to Armstrong, have publicly accused him of threatening them into silence over the years, and now after his public admission those claims are being taken seriously.

Investigators are reportedly looking into Armstrong's attempt to cover-up his drug use by allegedly threatening and interfering with potential witnesses, and not directly with his drug use, according to the ABC report.