TAMPA, Fla. — Hillsborough County’s sheriff is moving fast on what he calls a detestable incident.

A sergeant with the Hillsborough County Sheriff’s Office has been fired and was arrested Friday for aggravated assault with a deadly weapon.

Sheriff Chad Chronister says he has no idea why an exemplary employee with 21-years at the Hillsborough County Sheriff's Office pulled a gun on a prone suspect Thursday.

The sheriff says deputies mistakenly transported an arrestee from the jail to a mental health facility. The man left the facility and was found hiding behind a trailer.

Chronister says deputies took the man to the ground and had him a prone position when Sgt. Janak Amin kneeled next to the man, pointed a gun at his head, and threatened to shoot him if he didn't identify himself.

Chronister says other deputies intervened and told supervisors about what happened.

"I will always fight for and protect victims while relentlessly pursuing law breakers even if the law breaker is a law enforcement officer,” he said.

The sheriff says deputies had a rapid ID machine at the scene.

Chronister believes the sheriff’s office’s policy that requires deputies to intervene when they see a fellow deputy doing something wrong worked in this case.

Deputies are not releasing the man's identity due to Marcy's Law.