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Kevin Johnson and Doug Stanglin, USA TODAY

WASHINGTON --The FBI said Wednesday that there is no evidence that Navy Yard gunman Aaron Alexis targeted specific individuals in the shooting rampage last week in Washington, D.C., that left 12 people dead.

The FBI also released a video Wednesdasy of the 34-year-old shooter on the day of the Aug. 16 attack that shows him entering a Navy Yard building and walking the halls with a shotgun. Alexis was killed in a shootout with police.

Valerie Parlave, the FBI assistant director in charge of the Washington office, said Alexis was delusional and thought that extremely low frequency waves, or ELF, were controlling him.

She said at a news conference that the words "my ELF weapon" were written on the shotgun he used in the killings.

Parlave also said investigators are continuing to explore the background and motivations of the former Navy reservist and technology contractor, but noted that he had a well-documented history of mental health issues.