(Washington, DC) -- Video released by the FBI shows Aaron Alexis stalking the Washington Navy Yard with a shotgun, looking for people to shoot. Alexis killed 12 people last week before being gunned down by police. The FBI has also released pictures showing slogans etched into Alexis' shotgun. They include the phrases "better off this way" and "end to the torment." The FBI says it seems Alexis believed he was being influenced by electromagnetic waves. A document he left behind says, quote, "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."