Update 10:40 p.m. EDT: Washington, D.C., police have ruled out the possibility of a second shooter based on eyewitness accounts and security camera footage.
"We have now exhausted all means that we have available to either support or discount that lookout," Metropolitan Police Chief Cathy Lanier said in a live press conference. "We are comfortable we have the single and sole person responsible for the loss of life."
Update 7:30 p.m. EDT: CNN's Anderson Cooper reports that the FBI have ruled out a second shooter.
CNN's Evan Perez reports FBI investigators have ruled out any other shooters. All latest info in @AC360 8/10pm
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â€” Anderson Cooper (@andersoncooper) September 16, 2013
Washington, D.C., Mayor Vincent Gray said Monday evening there was no link to any terrorist group in the morning's Navy Yard shooting that left 13 dead, including alleged shooter Aaron Alexis.
Gray appeared alongside Police Chief Cathy Lanier in a joint news conference to deny any link to known terrorist organizations in Alexis’ shooting.
“We don’t have any known motive at this juncture,” Gray told Washington Post reporters. “We have no information that would suggest that’s the case at this point.”
Gray also asked people to stay on the lookout for a possible accomplice or second shooter, described as an African-American man in his 50s sporting gray sideburns and an olive drab uniform. Lanier stated that police and the FBI are still carrying out an active investigation into the shooting, stating that everyone in the Navy Yard has been asked to remain in place and under shelter.
The district's House delegate, Eleanor Holmes Norton, also appeared at the press conference to reassure residents that Washington is still a safe city and that citizens will be well-protected.
“This is the safest city in the United States. Not safe from attack, but safe,” she said at the press conference. ”This is a safe city and we can go about our business in the usual way.”
New details have also emerged concerning Aaron Alexis, identified as the Navy Yard shooter. Alexis, 34, was arrested in 2004 for shooting out the tires on a Seattle construction worker’s automobile, the Seattle Police Department reports. Alexis later claimed that he could not remember firing the shots during the “blackout.”
Three years later in 2007, Alexis enlisted in the Navy, where the New York City native served as an aviation electrician until 2011, according to military records. ABC News reports that Alexis was discharged under less-than-honorable circumstances after a series of misconduct issues. His last known residence was listed as Fort Worth, Texas, though the Washington Post speculates that he may have worked as an independent contractor for the Navy in Washington before the shooting.
FBI Assistant Director Valerie Parlave has asked that anyone with more information on Alexis or his motives call 1-800-CALL-FBI.
“No piece of information is too small. We are looking to learn everything we can about his recent movements,” she told the Washington Post.