Video of Aaron Alexis, the man who killed 12 people with a variety of firearms last week in Washington, D.C. and who was killed by police, has emerged.

With the phrase "end the torment" etched on his Remington 870 shotgun, the video captures Alexis pointing his gun in offices as well as stalking people in the building.

Authorities believe Alexis may have had mental problems based on documents found on his electronic devices.

An ultra low frequency attack is what I’ve been subject to for the last three months, and to be perfectly honest, that is what has driven me to this