The top special agent overseeing the FBI’s largest field office has been forced to retire, according to an email he sent to colleagues and obtained by CNN.

The head of the FBI’s New York field office who was reported to have resisted Justice Department efforts to scrutinize agents who participated in politically sensitive investigations has told coworkers that he has retired from the bureau after being directed to do so.

Two sources told NBC News that James Dennehy, a widely respected leader, was given the option to resign or be fired.