That indictment says Hutchins made the threat last Aug. 23, the same day Armstrong announced he wasn't going to fight the USADA sanctions for doping. "I have been subjected to a two-year federal criminal investigation followed by Travis Tygart's unconstitutional witch hunt," the cyclist said in a letter to the agency.
Both suspects in the threats cases have been arrested and are scheduled to make initial appearances in federal court in Denver on July 29.
Making threats via interstate commerce carries up to a five-year prison sentence and a $250,000 fine.
Shortly after Armstrong said he wouldn't fight the USADA sanctions, Tygart revealed he had received death threats and was asking the FBI to investigate.
In an interview with "60 Minutes" following the Armstrong penalties, Tygart said the death threats came anonymously via emails and letters. Asked if he remembered any specific threats, Tygart said, "The worst was probably puttin' a bullet in my head."
When news of the arrests went public, USADA chairman Edwin Moses released a statement thanking the FBI and U.S. attorney's office for handling the case.
No one answered the phone at numbers listed in public records for either Keats or Hutchins.
In August, USADA handed Armstrong a lifetime ban and stripped all seven of his Tour de France titles for running what Tygart called "the most sophisticated, professionalized and successful doping program that sport has ever seen."
Since then, Armstrong has admitted to doping and stepped down from the Livestrong Foundation, which raised hundreds of millions of dollars for cancer research based largely on the cyclist's popularity. Armstrong overcame testicular cancer before winning his first Tour de France and used his story as an inspiration for others battling cancer.