Video: Inside the Washington Navy Yard shooting

Newly released security camera footage shows Washington Navy Yard shooter Aaron Alexis running through the hallways at the Navy Yard with a sawed-off shotgun.

In the chilling closed-circuit video, Alexis is shown pulling into the compound in his car, calmly entering the facility with his shotgun stowed in a backpack and then prowling the hallways with the weapon out.

The FBI also disclosed on Wednesday that Alexis believed he was being controlled by electromagnetic waves in the months before he killed 12 people at the southeast Washington base on Sept. 16.

There are no indications that Alexis, 34, was targeting anyone in the rampage, said Valerie Parlave, the FBI assistant director in charge of the Washington field office.

"We have found relevant communications on his electronic media which referenced the delusional belief that he was being controlled or influenced by extremely low-frequency (ELF) electromagnetic waves for the past three months," Parlave said.

She added that Alexis had scrawled "My ELF weapon" onto his Remington 870 shotgun. "The etching ... is believed to reference these electromagnetic waves," Parlave noted.

Alexis, a government technology contractor, acted alone and was killed by police on the third floor of the yard's Naval Sea Systems Command headquarters, after exchanging fire with officers for an hour.

The shooting spree and the question of how Alexis got security clearance to enter the base have prompted calls for a review of government vetting of private contractors.

Wire services