After the USADA'S scathing report on systematic doping by Armstrong and his teams, he was stripped of his seven Tour de France titles and banned from elite sport for life.
Cycling body UCI has been accused of covering up suspicious samples from Armstrong, accepting financial donations from him and helping him avoid detection in doping tests.
During the Senate hearing, Tygart said he had "evidence of the UCI's involvement in this affair," and Armstrong could hold the key to revealing the extent of that involvement.
"Armstrong led us to believe during the course of our interaction with him that he had evidence of their complicity in this situation, and of course we've developed additional information that will come out through our process, that I can't comment on right now," Tygart said in an interview with The Associated Press.
Tygart, who said he last spoke with Armstrong about a month ago, hopes the rider changes his mind and details what happened during his reign as cycling's undisputed superstar.
"We're hopeful at some point he'll come in and be truthful. I think he could provide a lot of information," Tygart told the AP after speaking before the Senate for about 1 ½ hours. "We certainly are under the impression based on our conversations around our meeting back in December that he has information and evidence that would be extremely helpful and powerful in trying to set cycling on a new path."
After years of denials, Armstrong finally confessed to doping during an interview with Oprah Winfrey in January. Tygart thinks there is still much more to come and Armstrong has crucial information to share.
"Our firm belief is (he has) and obviously I wouldn't say that unless I had backing to say it," Tygart said. "We're convinced."
Tygart also wants the UCI to maintain its pledge made in November when it set up an independent commission to examine claims it had covered up suspicious samples from Armstrong and accepted financial donations from him. Two months later, the commission was disbanded.
"We're hopeful that (the UCI) are going to take decisive action and we're fully prepared to participate in a meaningful process, not a setup, a self-scripted outcome," Tygart told AP. "And if not through that, then it will be through the ongoing process that we're now involved with."
During his hearing, Tygart answered many questions concerning the alleged role the UCI played in covering up Armstrong's doping.
Tygart said the UCI was clearly "aware of several (suspicious) samples" returned by Armstrong at the 2001 Tour of Switzerland and 2002 Dauphine Libere race, and the six positive EPO samples from the 1999 Tour first reported by sports daily L'Equipe in 2005 but had "failed to proceed on any of this data."