"One indictment in the case lists 32 defendants, including the former N.B.A. player and coach Damon Jones and the Portland Trail Blazers coach Chauncey Billups, who are both charged with wire fraud conspiracy and money laundering conspiracy, according to the docket sheet in the case.
Many of the other defendants also face those charges, along with counts accusing them of operating an illegal gambling enterprise and conspiracies to commit extortion and robbery."
They don't necessarily have or need evidence that Billups was aware of the rigging, just the regular financial crimes of taking payments from the Mafia that will presumably get him to cooperate.