WHITE SETTLEMENT (CBSDFW.COM) – Authorities are doing everything they can to find out more about the gunman who shot and killed 12 people on Monday morning at the Washington Navy Yard. The suspect, 34-year-old Aaron Alexis, who was shot and killed during a shootout with police, once lived in North Texas.

The investigation into Monday’s deadly shooting at the Navy base continued into Tuesday morning, with the suspect’s motive still being the biggest question mark.

Police said that Alexis opened fire inside of a building at Washington Navy Yard. From his position on the fourth floor, he had a sniper’s view overlooking the atrium below. A total of 12 people were killed in the attack, all civilian contractors. Alexis became the 13th person to die in a shootout with authorities.

Alexis was a defense contract employee, and was working at the Washington Navy Yard on a computer wiring project. He used a valid pass to enter the complex. He had three weapons including a handgun, a shotgun and an assault rifle. The victims ranged in ages from 46 to 73 years old.

Omar Grant helped a visually impaired co-worker escape from the attack. “People ran out of the building,” he said. Now, he feels lucky to be alive. “I’m here with my family and I’m thinking of those people who aren’t.”

Since police cannot question Alexis, they are looking to the public for a better idea of the suspect’s whereabouts and activities leading up to the Monday morning shooting. “While we have learned some information about his recent whereabouts,” said FBI assistant director Valerie Parlave, “we continue to work to determine where he has been, who he has talked to and what he has done.”

The FBI released a poster on Monday asking the public for any additional information. “By putting that out,” said CBS senior correspondent John Miller, “they’ve already had numerous acquaintances come forward — former co-workers, current co-workers — and they’ve learned a lot.”

The suspect’s family said that Alexis had little to do with them, and that Monday’s events came as a surprise. “No one saw it coming,” stated brother-in-law Anthony Little. “No one knew anything. So, it’s just shocking.”

The FBI has also searched a Washington, D.C. area hotel where Alexis was believed to be staying in the days prior to the shooting.

Before heading to the nation’s capital, Alexis spent time living and working in Fort Worth. Those who knew him said that there were not any signs that he was capable of such violence. Alexis lived with the owners of the Happy Bowl restaurant for a year and a half. Employees there said that he had some problems, but became like a member of the family.

At the time, his father told police that Alexis struggled with PTSD after rescuing people in New York City during 9/11. Those who knew him in Fort Worth stated that he was angry about issues with his veteran benefits. There has been no word about whether or not that may have been part of his motive in Monday’s attack. “I knew that there was some things that Aaron was upset about with his veteran benefits,” said friend Kristi Suthamtewakul. “He wasn’t getting paid on time or he wasn’t getting enough. But it was nothing of this magnitude.”

Authorities do not believe that Alexis has ties to any terrorist organizations. He was previously arrested in 2004 in Seattle for shooting out a construction worker’s tires during what he described as “an anger-fueled blackout,” and then arrested again in 2010 in Fort Worth for firing shots into the apartment unit above his own. He was not prosecuted in either case. In the Fort Worth case, Alexis said that he was cleaning the gun when it accidentally went off.

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