(CNN) - Sen. Susan Collins, R-Maine, pressed for more answers Wednesday on why the Navy Yard shooter, who worked for a company contracted by the Navy, had been given security clearance despite his troubled past.
"We absolutely have to be asking tough questions. It appears that there was insufficient vetting by the contractor, that if it had been done would have revealed many of the red flags," Collins said on CNN's "New Day."
Aaron Alexis, who was killed Monday, certainly didn't have a clean past. He was arrested in 2004 for shooting out the tires of a car, and his Navy record included eight instances of misconduct. He was arrested in 2008 on a disorderly charge and was again taken in two years later for allegedly firing a gun through the ceiling of his apartment.
Navy spokesman Rear Adm. John Kirby told CNN Alexis "passed a routine security clearance back in 2007 when he enlisted. It was good for 10 years." Alexis was given a "secret" security clearance in March 2008, shortly after he joined the Navy in 2007.
He carried that clearance with him when he was honorably discharged in 2011, Kirby said, and could use it in another position so long as he is hired within two years. He was hired in 2012 by The Experts, the contracting company that led to his work at the Navy Yard.
Collins questioned the process that allowed Alexis to keep his clearance, asking whether contractors were "taking shortcuts that have led to people with criminal records, with serious mental illness, or who are otherwise unsuited for security clearances."
As a reservist Alexis was exempted from the periodic reinvestigation of clearance that active duty officers go through every 4½ years, or the polygraphs they go through every 2½ years.
Retired Navy officials and private experts have told CNN Alexis should not have been able to keep his clearance, given his troubled history.
Collins argued it was "truly inexplicable" that someone with his past could have clearance. She said she hopes the Senate Intelligence Committee, of which she is a member, will expand its investigation on NSA leaker Edward Snowden, also a contractor, to include a probe on Alexis. She said she's also in talks with the Senate Homeland Security Committee, which has jurisdiction over the Office of Personnel Management, to look at contracting policies.
Sen. Kelly Ayotte, R-New Hampshire, on Tuesday called for a hearing to examine federal contractor hiring practices at military installations.
"One step that can be taken immediately is ensuring that criminal data bases and the terrorist watch lists are always consulted," she added. "And that there's some sort of continuous monitoring that would pick up problems rather than waiting as long as five or ten years to review security clearances."
– CNN's Ashley Killough, Jake Tapper, Kevin Bohn, Gloria Borger, Brian Todd and Josh Levs contributed to this report.