The man who killed twelve people at a US Navy office building in Washington, DC believed he was being bombarded with radio waves, says the FBI, which also released chilling security video of the man.

Aaron Alexis is seen stalking the halls and stairwells of the building during his rampage.

On his shotgun, he had scrawled “My ELF Weapon!” referring to extremely low frequency radio waves Aaron believed were trying to control him.  Other phases scratched onto the weapons were “End to the Torment!” – “Not what yall say” – and “Better off this way,” according to investigators.  They also say Alexis acted alone.

Alexis was able to get access to the building because of the security clearance he received in 2007 for his job at a subcontractor. The background check was handled by yet another subcontractor – USIS, the same company that cleared Edward Snowden for top-level security access.  And look how that worked out.  USIS is under criminal investigation over whether it misled the government about the thoroughness of its background checks. Though not specifically in the Aaron case.