FALLS CHURCH, Va. -- A sheriff's deputy fatally shot a recently-released patient who threatened him with a metal signpost outside a northern Virginia hospital, authorities said Tuesday.

Fairfax County police chief Col. Edwin Roessler said Tuesday that hospital security had escorted the man to a bus stop Monday night on the Inova Fairfax medical campus in suburban Washington, D.C., just after his release from the hospital. They left, but responded again when security received several calls about a suspicious man at a bus stop with what appeared to be a weapon.

A Fairfax County Sheriff's deputy who was on the campus guarding an inmate being treated heard the call on radio traffic and responded along with hospital security, said Fairfax County Sheriff Stacey Kincaid. The deputy was in uniform and on duty for the unrelated guard assignment, but had jurisdiction to monitor radio traffic and respond to incidents, Kincaid said.

Roessler said the recently-released patient, a Hispanic man whose identity has not yet been released pending family notification, was in the midst of a "mental episode" and was swinging a metal signpost he had apparently pulled out of the ground on the campus. The man struck and injured a responding security guard, Roessler said.

The deputy responded and tried to negotiate with the man, but Roessler said the patient began "charging" at the deputy. The deputy gave him orders to drop the signpost and was trying to retreat, Roessler said, but the patient "kept on coming at him with the signpost in a cocked position, ready to strike."

That's when officials say the deputy fired multiple times. The man was struck and later died at the nearby emergency room.

Kincaid said the deputy is an 18-year veteran of her department and is trained in crisis intervention. He is on administrative leave per department policy. She didn't release his name, age or race.

Roessler said there is surveillance video of the incident that will be a "crucial" part of the investigation, but said the video won't immediately be released.

The injured security guard was treated and released, Roessler said. A 911 call was also placed to dispatchers and Fairfax County police responded shortly after the shooting.

Roessler couldn't say why the man was being treated at the hospital or whether it was related to mental health care. He also didn't know why hospital security had initially escorted the man to the bus stop, but he said it was "clear to us that in some way, shape or form, the adult male suffered some type of mental episode."

The county police department's major crimes division assumed responsibility for the criminal investigation and the sheriff's office will conduct an internal investigation.