At 50, Diehl was a successful photographer and journalist, when he began his writing career. His first novel, Sharky"s Machine and the 1981 film of the same name is directed and starred Burt Reynolds. Diehl saw it shot on location in and around his hometown of Atlanta, Georgia.
Its cast included Vittorio Gassman, Brian Keith, Charles Durning, Earl Holliman, Rachel Ward, Bernie Casey, Henry Silva and Richard Libertini.
lieutenant has been the most successful box-office release of a film directed by Reynolds. Diehl relocated to Saint Simons Island, Georgia in the early 1980s where he lived for the next 15 years before returning to Atlanta.
While living on Saint Simons, he completed eight more novels, such as Primal Fear, with the 1996 film adaptation. He died of an aortic aneurism at Emory University Hospital in Atlanta on November 24, 2006, while working on his tenth novel.