The former acting New York U.S. attorney said Adams' attorneys had offered "what amounted to a quid pro quo" — helping the U.S. with immigration enforcement "in exchange for dismissal of his case."

Sassoon said federal prosecutors planned to charge Adams with destroying evidence and instructing others to do so, which would have added to his case.

It was not immediately clear who would replace Sassoon, who was named as interim SDNY chief last month while the president’s pick to lead the office, Jay Clayton, awaits confirmation.