McLEAN, Va. (AP/WAVY) — An off-duty U.S. Park Police officer fatally shot another off-duty officer in a Virginia apartment in what local authorities are describing preliminarily as an unintentional shooting involving alcohol.

Fairfax County detectives determined that the officer pulled the trigger on a gun he believed was unloaded early Sunday, striking Jesse Brown Hernandez inside an apartment on Old Meadow Road in McLean, Virginia, according to a police statement.

Officers arrived around 12:20 a.m. to find Hernandez, 22, deceased with a gunshot wound to the upper body, Fairfax County police said.

Police charged 25-year-old Alexander Roy with involuntary manslaughter. He is being held at the Fairfax County Adult Detention Center on no bond.

Police said that preliminarily detectives determined that the officer “was attempting to dry fire a firearm.”

“Dry firing is when one simulates the discharge of a firearm by pulling the trigger of a firearm that is unloaded,” police said in the news release.

There were four people in the apartment at the time of the shooting, and all were known to each other, police said. Three of the four involved individuals were off-duty U.S. Park Police officers.

Detectives continue to investigate the circumstances leading up to and surrounding the shooting, authorities said.