Nightly News   |  September 19, 2013

Police called 20 minutes after Navy Yard shooting began

New evidence is emerging in the shooting that killed 12 in the Washington, D.C. Navy Yard. It wasn’t until nearly half an hour after the carnage began, the FBI says, that the first officers to enter the building had the shooter in their sights. And the FBI now says that there is no evidence Aaron Alexis fired from the upper floors of the building down into the atrium below. NBC’s Pete Williams reports.

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This content comes from Closed Captioning that was broadcast along with this program.

>>> good evening. while americans are still absorbing the blunt force of this latest mass shooting, tonight a lot of the details of what we thought we knew about the gun massacre at the washington, d.c. navy yard have changed. the new director of the fbi briefed a group of journalists today including our justice correspondent pete williams and he laid out a version of event s that differs from what we were first told and first reported. pete is with us tonight from our d.c. newsroom to start us off. hey, pete. good evening.

>> reporter: brian, good evening. the fbi director james comi says video and physical evidence show nearly half an hour passed from the time the shooting started to the time officers found aaron alexis and fired back. the fbi director says alexis began firing shortly after 8:00 a.m . in a fourth floor hallway. comey says alexis was wandering the halls, hunting for someone to shoot with no signs of targeting anyone in particular. the first call for help didn't come until 8:21 with units then dispatched.

>> we had a report on the fourth floor, a male with a shotgun, multiple shots fired. multiple people down.

>> reporter: alexis continued shooting in upper hallways. comey said he fired the shotgun and then switched to the handgun. there is no evidence, the fbi says, that alexis fired from the upper floors down into the atrium below. but it wasn't until half an hour after the shooting started, the fbi says, that the first officers to enter the building found him and had him in their sights.

>> they could hear gunfire. because of the size of the building, difficult to pin down where the gunfire was coming from.

>> reporter: after walking past the dead and injured, two officers finally located alexis inside an office, hidden among a maze of cubicles.

>> there was carnage everywhere in this building. absolute carnage. when officers have to go past people who are asking for help because they still have yet to neutralize the threat that weighs heavy on your mind.

>> reporter: officials praised the prompt action of first responders but a navy police union says the force was understaffed preventing quicker action. a member of a u.s. capital tactical team say they were preparing to help but were order ed back.

>> i asked the capital police board to do an independent fact review of the allegations to find out exactly what happened.

>> reporter: also tonight michael isikoff reports the navy security clearance check for alexis was done by the same private firm who did the check for edward snowden who join the nsa where he stole and leaked hundreds of classified documents.

>> pete williams with the latest from washington tonight. thanks.