A civilian who disarmed a guard and fatally shot a sailor on a docked destroyer before being killed himself entered the base on a tractor-trailer with a transportation worker's credential, according to the Navy and a military official.
Navy officials were still searching for answers Wednesday about what might have motivated the civilian, who has not been identified. The civilian was shot and killed late Monday night by Navy security forces -- a sailor assigned to the USS Mahan, said the military official, who spoke on condition of anonymity because the person was not authorized to publicly release the information about the civilian or the victim.
The civilian was authorized to be on Naval Station Norfolk, the Navy's largest base, but it wasn't immediately clear for what reason or why he would want to approach the guided-missile destroyer, which shares a pier with a hospital ship, the USNS Comfort.
The Navy said the civilian was coming toward the ship's quarterdeck, which is traditionally the ceremonial entry point of a ship, when he got into a struggle with the Petty Officer of the Watch, whom he was able to disarm.
The sailor who was killed was the chief of the guard, a security role, the military official said. The Navy has not released his name, but his father told The Associated Press on Wednesday that the victim was his son, sailor Mark Mayo of Maryland.
Mayo, 24, had been a military policeman since completing training in 2008, and he patrolled the Norfolk base, his mother, Sharon Blair, told The Herald-Mail newspaper (http://bit.ly/1fhiiSs). He spent his adolescence in Hagerstown, Md., she said.
In the Navy, law enforcement duties are performed by a master at arms. Those sailors can be assigned to ships or shore installations and can perform a range of duties, such as oil platform protection, physical security inspections and training security force personnel.
A Navy job description says they usually undergo nine weeks of initial training, where they learn anti-terrorism techniques, armed sentry standing techniques and physical restraint techniques, among other things.
Decondi Mayo said Navy representatives told him during a visit Tuesday that his son had been killed.
No other injuries were reported from Monday's encounter on the ship.
On Wednesday, the Navy appointed Rear Adm. Jeffrey Harley to lead an investigation into the circumstances surrounding the shooting. Harley's role will be different from that of criminal investigators, and will include a review of applicable policy, programs and implementation, according to the Navy.
To get onto the base, civilians must be escorted or have identification that allows them to be there. Authorized civilians include Department of Defense employees, contractors and military family members.
Capt. Robert Clark, Naval Station Norfolk's commanding officer, said Tuesday that identification found with the civilian indicates it is unlikely he was a military dependent authorized to be on base for that reason.
Clark said the civilian was found with a TWIC card, a transportation worker's credential issued by the Transportation Security Administration to personnel such as truck drivers who require unescorted access to secure areas. But he said it was unclear what exactly the civilian's job was or when he worked on the base.
All merchant mariners are required to have a TWIC card, including employees of the Navy's Military Sealift Command, which hires civilians to crew its ships, including the USNS Comfort. The cards are valid for five years, according to the TSA.
Each base entrance is guarded, and motorists present IDs. Inspections are rare, and Clark noted that the civilian did not bring a weapon on base.
Clark said the base would review its security procedures but also said the Navy's response shows that "force protection is working."
All 13 piers have additional security forces that guard access. As part of ongoing security efforts, handheld ID scanners were implemented this year at Navy bases in the region, including the Norfolk station.
The shooting on the Mahan comes about a month after the Navy held anti-terrorism and force protection exercises on bases across the U.S., including an active-shooter drill at Naval Station Norfolk. And it follows a September incident at the Washington Navy Yard, in which a gunman -- identified as a contractor and former Navy reservist -- killed 12 civilian workers before being shot to death.
The Norfolk base was briefly on lockdown after the Monday night shooting but resumed normal operations aside from the Mahan's pier Tuesday. On social media, many of those who had connections to the ship or sailors aboard it changed their profile pictures to the ship's emblem.
Naval Station Norfolk covers more than 6,000 acres and is the home port for 64 ships, according to information the Navy provided in February. About 46,000 military members and 21,000 civilian government employees and contractors are assigned to the base and its ships, according to the Navy figures.
Associated Press writer David Dishneau contributed to this report from Hagerstown, Md.