The FBI released new video surveillance today of Aaron Alexis, the Washington D.C. Navy Yard gunman who killed 12 innocent people and injured three others. The footage reaffirms the weapon of choice authorities suspected Alexis used — a shotgun — and that he parked his car in the garage, entered through the front door, and proceeded to creep through the building picking off people along the way.

You can watch the FBI released video footage here: WARNING — Video may be disturbing to some viewers

The sawed-off shotgun bore the etchings “Not what y’all say” and “Better off this way,” among others, thought to be at the hand of Alexis and alluding to his mental illness.

The 34-year old former Navy Reserve member and defense contractor suffered from a history of mental illness that culminated in him hearing imaginary voices, an affliction he credits to post traumatic stress that he incurred after the September 11, 2001 World Trade Center tragedy.

Alexis also showed a history of gun violence, having once shot out the tires of a construction worker’s car during a self-described rage blackout and having discharged his weapon through the floor of his apartment and subsequently through the ceiling of the tenant that resided below him.