Plenty were proven guilty. They were just rich enough to get away with it.
Birkenfeld was sentenced in August of 2009. UBS paid $780 and avoided all criminal charges. Individuals have since been fined or put on probation, or set free... except for Birkenfeld.
Extremely wealthy tax evaders can afford to pay measly slap-on-the-wrist fines for their crimes. $780 million for UBS is a complete joke compared to the billions in evaded taxes.