( CNN ) -- A civilian boarded a U.S. Navy destroyer at the world 's largest naval base , took a gun from a Navy guard and used it to fatally shoot a sailor before security personnel shot and killed him Monday night , Naval Station Norfolk 's commanding officer told reporters Tuesday . The shooting happened at about 11:20 p.m. aboard the USS Mahan , which was docked at the Virginia base 's Pier 1 , Capt . Robert Clark said . The civilian -- a man -- had credentials to be at the base and the pier , having `` worked at the installation at a previous time , '' Clark said . He added he believed the credentials did `` not necessarily '' allow him to be on the ship , and that investigators were trying to determine whether he had a current assignment at the base . The names of the people involved in the shooting were not immediately released . The Navy was trying to inform the sailor 's family about his death , Clark said . The man was approaching the quarterdeck when sailors working security confronted him , Clark said . During a struggle , the man disarmed the petty officer of the watch , he said . He used the petty officer 's gun to shoot and kill a different sailor who had come to help , Clark said . `` Naval Security Forces then killed the suspect , '' Clark said . Clark emphasized that the man was not armed when he entered the base . Clark said he did n't know why the man was there Monday night , and he did n't provide details about the nature of his previous work at the base . The civilian had credentials to be on the base but breached security to get on the ship , a U.S. defense official told CNN earlier Tuesday , speaking on condition of anonymity . Naval Station Norfolk was briefly locked down after the shooting . Clark said officials would examine the base 's security procedures because of the shooting . Washington Navy Yard shooter raised concern previously , but military said it was n't told . CNN 's Tina Burnside and Jonathan Helman contributed to this report .
Civilian had ID to get on base but breached security to leave ship , official says . Shooting occurred on the destroyer USS Mahan , commanding officer says . The shooting happened at Building 1 of Naval Station Norfolk in Virginia . Official : Shooting happened after civilian fired gun from sailor who was on guard duty .