(NBC NEWS)-- More details are emerging about the man believed to have killed a dozen people in Washington Monday. There's mounting evidence he suffered from severe mental illness.
The investigation spans coast to coast, and many questions still remain. In light of his past, lawmakers and investigators still want to know how Alexis could be allowed to get onto the base, and whether he should have been allowed to buy a gun.
As Washington remembers the victims. "That's a hole that just will never be filled," said Kathleen Gaarde's Husband, Douglass Gaarde.
The FBI is tracking every move Aaron Alexis' made. "How did he plan the attack? How did he get the weapons?" asked U.S. Attorney Ronald Machen.
"It was a lawful purchase of a shot gun made in Virginia," declared the FBI's Valerie Parlave.
Legal - even though the Veterans Administration was treating him for mental illness. Less than a month ago Alexis reported hearing voices. "I have no idea how he got clearance from Navy Yard to have those weapons," said John Rogers, Johnson's Wife Judy Johnson.
He got them because it's illegal for the VA to report treatment. And as a contractor, he had a 10-year security clearance. "It's not that difficult to get a security clearance if you do not have major red flags in your background," said Security Analyst Roger Cressey
The incident is raising more talk about gun control: "We do not have a firm enough background-check system," said President Barack Obama
"We've got to have the votes first. We don't have the votes," said Senate Majority Leader, Senator Harry Reid (D-NV),
And it's raising questions about base security.
Lawmakers want more details on a Pentagon report that questions whether the government cut corners and put bases like the Washington Navy Yard at risk.
Meanwhile, the Secretary of the Navy has ordered a review on security and how those clearances are granted.