When I was in they had begun using Pier and Liberty Passes specific to your ship. You had your active duty military ID and a Liberty or Pier pass with your name and ships name on it you needed to get onboard ship. Pier Pass required a working or dress uniform it meant you were on duty like watch, taking off the trash or other task. In the yard you had a third required I.D. in the form of an ID pouch. A ship that small? Petty Officer of the Watch {Brow Watch} likely knew he didn't belong there.
Well, this guy had base access for sure, we know that now. But he was stopped while trying to get aboard the Mahan by the PO at the check station. He struggled with him, overcame him and took his gun, and then shot and killed a sailor running up to help the PO. Then other security onboard ship killed him there on deck too.
I do not believe he had any business on the Mahan, and was apparently not being allowed aboard.
I’d like to know what the real story is and will check with folks I know over in Norfolk to see what they say.