WASHINGTON - US lawmakers are calling for a review into how the suspected shooter in Monday's rampage at the Washington Navy Yard received and maintained a security clearance, despite a history of violent episodes.

Aaron Alexis, 34, received a security clearance more than five years ago and it helped him obtain his most recent job as a technology contractor at the Navy Yard, where he allegedly killed 12 people before being shot dead by police.

Lawmakers say this most recent incident shows serious flaws in the federal government's process for issuing security clearances and vetting contractors - an issue laid bare earlier this year by former National Security Agency contractor Edward Snowden who disclosed details about top-secret US spying programs.

Democratic Senators Claire McCaskill and Jon Tester plan to send a letter to the Office of Personnel Management's inspector general, demanding answers about how Alexis' background check was conducted for his security clearance.

The OPM is the agency primarily responsible for overseeing federal background checks.

"I want to know who conducted his (Alexis') background investigation, if that investigation was done by contractors, and if it was subject to the same systemic problems we've seen with other background checks in the recent past," McCaskill said in a statement to Reuters on Tuesday.

"While guilt ultimately lies with the perpetrator of this terrible crime, those who lost loved ones and were injured in yesterday's shooting deserve to know the answers to these questions," she said.

One of the points they want reviewed, according to a copy of the letter seen by Reuters, was "how Mr. Alexis' background investigations addressed his pattern of misconduct, including his reported arrests on charges relating to firearms in 2004 and 2010" and a prior disorderly conduct charge.

The OPM inspector general's office and OPM had no comment on Alexis.

Scrutiny of the security clearance process is just one security area that officials are reviewing in the aftermath of Monday's mass shooting.

US Defense Secretary Chuck Hagel is seeking a review of physical security and access at all Defense Department installations worldwide, and the White House said it will review standards for federal government contractors.