The gunman who slaughtered 12 people last week in Washington is seen darting through a navy building like a special forces operator in chilling footage released by the FBI.
The agency also said analysis of Aaron Alexis's medical history shows he believed he was being controlled or influenced by extremely low frequency, or ELF, electro magnetic waves.
He used a sawed-off shotgun in the September 16 massacre at the Washington Navy Yard and etched into various parts of the gun were several phrases, Valerie Parlave, assistant director of the FBI's Washington field office, said.
"On the left side were the phrases, quote, 'better off this way,' closed quote and quote, 'my ELF weapon,' closed quote," she told a news conference.
Police eventually shot and killed Alexis, but not before he killed 12 people.
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
"At this point, I can confirm that there are multiple indicators that Alexis held a delusional belief that he was being controlled or influenced by extremely low frequency or ELF electro magnetic waves," Parlave said.
"The etching of 'my ELF weapon' on the shotgun is believed to reference this."
Alexis was a 34-year-old former sailor with a history of disciplinary problems and brushes with the law. He had a security pass to get into the navy complex building because he was working for a navy contractor.
Parlave also said that etched into the barrel of the shotgun were the words "end to the torment" and etched into the right side of the shotgun receiver were the words "not what y'all say".
Video released by the FBI shows Alexis, wearing dark pants and a purple short-sleeved shirt, darting stealthily through empty hallways at a building of the Washington Navy Yard complex the day of the massacre.
At one point he seems to take cover at a corner in a hallway and peeks around to see what lies ahead, then takes off, walking fast. He is not seen opening fire in any part of the footage.
Another piece of video shows him walking through the front door of building 197 at the yard carrying a sort of gym bag.
"There are indicators that Alexis was prepared to die during the attack and that he accepted death as the inevitable consequence of his actions," Parlave said.
She said there is no evidence he targeted specific individuals.
