The White House and lawmakers said they want to tighten up the vetting of independent defense contractors after a former Navy reservist killed 12 workers at the Washington Navy Yard, just blocks from the Capitol.

Aaron Alexis, a computer contractor from Texas honorably discharged by the Navy in 2011, shot and killed a dozen civilian workers and wounded several others at the complex's Building 197, headquarters for the U.S. Naval Sea Systems Command. Alexis, 34, died following a shootout with police.

How Alexis, who was being treated for mental illness and had a troubling past, landed a contracting job that granted him access to a high-clearance building is a major concern as Washington deals with the fallout. Alexis had two run-ins with police over misfired weapons, though he was never charged, and had at least eight misconduct incidents while a Navy reservist.

“Twice this guy used weapons inappropriately. When you pull a gun out and blow a guy's tires out, that's a pretty dramatic misuse of a weapon,” said Sen. Lindsey Graham, R-S.C., describing one of Alexis’ prior gun incidents. “The fact that nothing happened is surprising and the fact that it never got reported in the system is deeply troubling.”

The Government Accountability Office has warned Congress for well over a decade, even before the Sept. 11 terrorist attacks, that access by poorly vetted civilian contractors to defense facilities posed a national security threat.

Shoddy background checks became a high-profile issue earlier this year after the massive leaks of classified information by National Security Agency contractor Edward Snowden.

President Obama announced he would review security measures for government contractors in the wake of the D.C. shooting.

A damning audit released by the Department of Defense Inspector General warned that the Navy's approach to background checks put the military branch at risk of a tragedy like the Navy Yard shooting. The report revealed that the Navy tried to cut costs by skipping or watering down security measures, including FBI background checks designed to weed out terrorists.

The audit found that the Navy had granted security clearance to 52 contractors with felony convictions. In cases in which contractors were vetted, background checks were often limited to a simple and unreliable review of public records. In some instances, civilian workers were able to access buildings even after their contracts expired.

The audit, which had been scheduled to be released this month, also said that some naval officials sounded the alarm that the system used for background checks, Rapidgate, was deeply flawed. Investigators warned that the cost-cutting measures were “placing military personnel, dependents, civilians and installations at an increased security risk.”

Naval command disagreed with the report’s recommendations to stop the use of Rapidgate and to provide funds so that Navy installations could gain access to an FBI anti-terrorism database. In a response to the auditors, Navy officials said stronger vetting procedures would slow business and “would not be feasible in a time of austerity.”

Sen. Tom Carper, D-Del., said he expects that the Homeland Security Committee he heads will explore enhanced background checks for contractors. A staff member for Republicans on the House Armed Services Committee said lawmakers are interested in discussing whether background checks for contractors should continue to be done by outside firms or by the uniformed services.

But the staffer also noted that resources are shrinking and there are thousands of jobs that require cleared personnel.

“That creates tension that can only cause problems,” he said.

Bradley Moss, a lawyer who specializes in national security and clearance issues, said Alexis wasn’t necessarily a candidate for having his credentials revoked. He was receiving the necessary psychiatric treatment and neither of his past criminal incidents resulted in charges, according to reports.

“There's no way to truly ever predict who is going to snap,” Moss said. “If you prevented everyone who ever had a red flag from working in a classified environment, you'd have 10 people working in the government. Everyone has something.”

Congressional Correspondents Tim Mak and Susan Ferrechio contributed to this report.