BOSTON (CBS) – Prosecutors have  asked a federal judge to force Whitey Bulger to prove he was granted immunity before his trial next June.

In court documents filed Friday, prosecutors say Bulger failed to provide any evidence of his claim that he had been granted protection from late U.S. Attorney Jeremiah O’Sullivan, in exchange for information Bulger provided the FBI as an informant.

Prosecutors say there’s no proof that Bulger and O’Sullivan ever met.