The FBI on Wednesday released surveillance video of Washington Navy Yard shooter Aaron Alexis as he entered the facility and walked some of its hallways with a sawed-off shotgun.
Authorities say Alexis shot and killed 12 people and wounded four others Sept. 16 before he was killed during a shootout with police. He left a note saying he had been subjected to an "ultra low frequency attack" and that it was the reason for his rampage. Authorities also detailed some of the etchings they say Alexis made on his shotgun.
Below is the footage released by the FBI on its official YouTube channel.