On Wednesday, a US sailor killed 2 workers before taking his own life at the Pearl Harbor military base near Honolulu in Hawaii.
According to the officials, the gunman also wounded the 3rd worker before he killed himself.
The incident prompted a lockdown at Joint Base Pearl Harbor-Hickam, which is on the Hawaiian island of Oahu.
The shooting was reported at about 14:30 (00:30 GMT) local time. The identities of those involved in the shooting have not yet been confirmed.
The officials said that all 3 victims were civilian defence department employees and the survivor is in stable condition.
Rear Admiral Robb Chadwick, speaking at a press conference, said it was unclear if the victims were targeted or shot at random.
He said the gunman has tentatively been identified as an active-duty serviceman assigned to the USS Columbia.
"Obviously our thoughts are with the families of the victims and everyone involved," Rear Adm Chadwick added.