Transcript for Navy Yard Shooter Caught on Tape Before Rampage
Let's get to the chilling new video of the navy yard shooter. You see the gunman here, stalking the halls in search of his next victim. Abc's pierre thomas is in washington with more. Good morning, pierre. Reporter: Good morning, robin. The images are disturbing. In those recent mass shootings, we've not seen the ugly reality of the victim's face in the final moments. Today, we do. They are the haunting final moments before aaron alexis begins his killing spree. All captured in chilling, living color. We first see alexis just before 8:00 a.M., Showing his entry pass before being waved in by a security guard. He drives into this parking garage. And moments later, walks into the navy yard through the front door of building 197. It's 8:08 a.M. No metal detector. No bag check. Somewhere hidden, he is carrying this sawed-off shotgun. The fbi says he goes to this bathroom stall on the fourth floor. Takes out the weapon. And reemerges, intent on killing. He's armed. Peeking around corners. Checking doors. Looking for someone, anyone to ambush and murder. He appears methodical, calm, driven. He moves quickly down the stairwell. And watch as he ducks behind the wall, after spotting potential victims at the end of the hall. Look at the body language, his intent is clear. She he's hunting. He was able to obtain a firearm two days before he carried out attacks. Reporter: On the shotgun, alexis carved, end to the torment. Better off this way. And my e.L.F. Weapon. Alexis held a delusional belief he was being controlled by e.L.F., Electromagnetic waves. Reporter: On computer files from his backpack, they find his final message. Ultra-low frequency attack is what I've been subject to the last few months. And that's what driven me to this. This meant killing 12 innocent people and wounding 4 more. The release of the video is sparking some controversy. At least one family telling cnn overnight, they were angry they were not told beforehand. Robin?
This transcript has been automatically generated and may not be 100% accurate.