The same company that investigated alleged Navy Yard shooter Aaron Alexis for his security clearance also did a 2011 follow-up investigation of Edward Snowden, the former NSA systems analyst who leaked documents about the National Security Agency.

The company, USIS, said in a statement Thursday it conducted Alexis' background check in 2007 for the Office of Personnel Management but that it couldn't elaborate.

"Today we were informed that in 2007, USIS conducted a background check of Aaron Alexis for [the Office of Personnel Management]," spokesman Ray Howell said. "We are contractually prohibited from retaining case information gathered as part of the background checks we conduct for OPM and therefore are unable to comment further on the nature or scope of this or any other background check."

USIS is under a federal investigation into possible criminal violations involving its oversight of background checks, the AP reported in July. USIS dominates the background check industry, taking in $195 million in government payments last year and more than $215 million this year.

Alexis had worked for a Florida-based IT consulting firm called The Experts. He had been refreshing Pentagon computer systems, holding a military security clearance that would have expired five years from now.

Alexis' employer said it had had no personnel problems with him and two separate background checks revealed only a traffic violation. But there were trouble signs below the surface. Public records databases used in those kinds of searches can be spotty repositories of arrest records, court dockets and other information.

The Experts — and possibly the government — missed how, in September 2010, Alexis' neighbor called police in Fort Worth, Texas, after she said she was nearly struck by a bullet shot from his downstairs apartment. When police confronted Alexis about the shooting, he said he was cleaning his gun when it accidentally discharged. Alexis was arrested on suspicion of discharging a firearm within city limits.

The checks also missed how, six years earlier, Seattle police arrested Alexis for shooting the tires of another man's vehicle in what he later described as an angry "blackout." Police said two construction workers reported seeing a man, later identified as Alexis, walk out of the home next to their worksite, pull a gun from his waistband and fire three shots into the rear tires of their car before he walked back home.

No charges were filed in either the Fort Worth or Seattle incidents.

The Experts said it had most recently used a company called First Advantage of Alpharetta, Ga., to search Alexis' past for criminal involvement. A First Advantage spokeswoman said Thursday The Experts asked only for a typical employment background check that only returns information on convictions, not merely arrests.

Navy Secretary Ray Mabus announced Wednesday that he wants three rapid reviews of security clearance procedures completed by Oct. 1, including a review of Alexis' service record to determine whether his conduct problems while in the Navy should have threatened his ability to keep his clearance.

The announcement came after Defense Secretary Chuck Hagel ordered a review of the physical security and access procedures at all U.S. defense facilities worldwide as well as a study of the programs used for granting and renewing the security clearances for the military, civilian employees and contractors.

"Obviously, there were a lot of red flags" about Alexis, Hagel told reporters at a Pentagon briefing Wednesday. "Why they didn't get picked, why they didn't get incorporated into the clearance process, what he was doing, those are all legitimate questions that we're going to be dealing with."

Hagel, facing mounting questions from lawmakers and the public over the military's security procedures, said he has ordered two Pentagon reviews. One will examine the physical security and access procedures at DoD facilities around the world. The other will examine the procedures for granting and renewing security clearances, including to contractors. Hagel said an independent panel will also look at those issues, while the Navy conducts a review of its own.

Military leaders are under pressure to account for how Alexis was able to both keep his security clearance -- despite a history of disturbing and violent behavior -- and walk into the military facility with a shotgun.

The Associated Press contributed to this report.