John Michael Callahan served in law enforcement for 44 years. His career began as a special agent with NCIS. He became an FBI agent and served in the FBI for 30 years, retiring in the position of supervisory special agent/chief division counsel. He taught criminal law/procedure at the FBI Academy. After the FBI, he served as a Massachusetts Deputy Inspector General and is currently a deputy sheriff for Plymouth County, Massachusetts. He is the author of two published books on deadly force and an upcoming book on supervisory and municipal liability in law enforcement.