An intense FBI investigation to uncover the motive of the Washington Navy Yard shooter is underway as new information indicates that shooter had a history of disturbing behavior.
On Tuesday, investigators began piecing together clues behind the massacre. Thirteen people, including the assailant, died and eight people were wounded in the shooting rampage.
Among the victims who died are 51-year-old Arthur Daniels, a grandfather of nine, and Kenneth Proctor, 46, who worked for the government for 22 years.
The shooter, 34-year-old Aaron Alexis, was a civilian contractor and former Navy reservist who received an honorable discharge.
He suffered from a host of serious mental problems, including paranoia, and was hearing voices in his head. He had been undergoing treatment from Veterans Affairs.
The FBI went through the shooter's rental car and visited a nearby Residence Inn where he'd been staying.
Does Congress desire to re-ignite the gun law debate? Dan Gainor, vice-president of business and culture at Media Research Center, answers this and more on CBN Newswatch, Sept. 17. Click play above to watch.
Concerned Veterans for America's Jessie Jane Duff, a retired Marine gunnery sergeant, spoke about base security and the immediate calls for gun control, on CBN News Channel, Sept. 17.
"We're looking to learn everything we can about his recent movements, his contacts, and his associates," FBI Assistant Director Valerie Parlave said.
Alexis also had a valid pass and security clearance to enter the Navy Yard. If the Navy had declared him mentally unfit, Alexis would have lost his security clearance.
He used a shotgun and two handguns before being gunned down by police. Officials have yet to explain why a man with so many serious mental issues still had a top security clearance.
The suspect's father once described his son as having anger management problems. Investigators have also learned Alexis had a history of disturbing behavior.
In 2010, he was accused of recklessly discharging a firearm into a neighbor's apartment. And in 2004, he confessed to shooting out the tires on another man's car.
But Alexis was not a loner, and his friends were shocked to hear he'd gone on a shooting rampage.
"I couldn't believe that he did that. He's not that kind of guy to kill people," Alexis' friend, Nutpisit Suthamtewakul, said.
Former roommates who lived with the suspect in Texas earlier this year say he was a practicing Buddhist. They also say he's been upset with the military since being discharged in 2011.
"He was just upset with the government and all that. He just felt slighted by his benefits -- by just what he was getting each month," said Kristi Suthamtewakul, another of his friends.
Meanwhile, the deadly shooting has reignited talk about gun control on Capitol Hill.
"Congress must stop shirking its responsibility and resume a thoughtful debate on gun violence in this country," Sen. Dianne Feinstein, D-Calif., said.
But not everyone agrees. Jessie Jane Duff, with Concerned Veterans for America, told CBN News that more laws aren't the answer.
"Gun control laws only allow criminals to get ahold of the weapons and those who are honorable people, like myself, wouldn't be able to defend ourselves, so that is a misnomer, it's not even a fact-based argument," she said.
It's still unclear how Alexis was able to get an assault style rifle inside the Navy Yard. Security requires visitors to pass through turnstiles monitored by security guards before entering.
Investigators say they're confident Alexis was the only shooter.
Meanwhile, at the Navy Memorial in downtown D.C., Defense Secretary Chuck Hagel and other officials paid their respects to the victims of the Monday Navy Yard shooting.