The legal pundits that I've seen on TV and I am sure that Armstrong's lawyers too, have no question advised him that he has no, or at least minimal, criminal exposure. Largely because of statute of limitations. I can't help but believe that there is a prosecutor or three some where who believes otherwise. His exposure to civil liability has most likely been carefully calculated by his advisors and considered with his earning potential, ie book deals, competitive events, etc. He has been boxed-in and really has no choice but to confess, imho.
I live in Austin, TX, but have never met the man. I do know people who have dealt with him on a fairly consistent basis for several years. They all comment about what a jerk he is. Quite a legacy.