An off-duty U.S. Park Police officer fatally shot another off-duty officer after police say he pulled the trigger on Thomas Caldwella gun he thought was unloaded.

Police responded to a call of a person shot in McLean, Virginia, about 10 miles west of Washington, D.C. and found Jesse Brown Hernandez, 22, dead inside his apartment with a gunshot wound in his upper body, according to a news release from Fairfax County Police Department.

Officials found that Alexander Roy, 25, attempted to dry fire a firearm and unintentionally shot Hernandez. Police believe that alcohol played a factor in the unintentional shooting.

Dry firing is when someone pulls the trigger of a firearm that is not loaded. Police believe that Roy did not realize that the firearm was loaded when he accidentally shot Hernandez.

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Four people were in the apartment at the time of the shooting; three of the individuals were off-duty U.S. Park Police officers, police said.

Roy was charged with involuntary manslaughter, police said. He is being held at the Fairfax County Adult Detention Center on no bond.

Fairfax County police are asking that anybody with information about the shooting should contact the department.