USIS, under criminal investigation over whether it misled Washington about its background checks' thoroughness, originally denied it did a check on Alexis, The Washington Post said.
Alexis, a former Navy reservist, killed 12 people at the Navy Yard Monday before being killed by police. Union representatives for first responders said Thursday radios for federal firefighters and police officers failed during the initial response, forcing officers "to use their cellphone to just call out and tell them what's going on," Anthony Meely, chairman of the Fraternal Order of Police Naval District Washington Labor Committee, told The Hill.
The investigative company -- the largest private provider of government background checks -- explained its reversal by saying it got new information Thursday.
"Today we were informed that in 2007, USIS conducted a background check of Aaron Alexis for [the U.S. Office of Personnel Management]," the Falls Church, Va., firm, said.
Alexis joined the Navy in 2007.
"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," said the company, which was OPM's investigative branch until it was spun off in 1996 as U.S. Investigations Services Inc.
It's now part of Altegrity Inc., owned by Providence Equity Partners LLC.
Alexis had a secret security clearance that let him get an access card needed to get onto the Navy base. Such clearances typically remain valid for 10 years.
There is no indication USIS did anything wrong when it vetted Alexis, OPM said in a statement.
OPM has "reviewed the 2007 background investigation file for Aaron Alexis, and the agency believes that the file was complete and in compliance with all investigative standards," said OPM's Federal Investigative Services division, which handles security checks for most federal agencies.
Government officials said this week the 2007 background check uncovered a 2004 incident when Alexis shot out a car's tires of a car, the Post said. The incident was considered "malicious mischief."
Later run-ins with law enforcement and reports of potentially serious mental-health issues occurred years after the 2007 background check.
USIS also handled the background investigation of National Security Agency leaker Snowden, who faces U.S. government charges, including espionage, and fled to Russia.
USIS told The Wall Street Journal three weeks ago the federal government raised no concerns about its work when it conducted a five-year "periodic re-investigation" of Snowden in February 2011.
The company said the NSA, not USIS, was ultimately responsible for approving or denying Snowden's security clearance.
USIS has been under investigation since late 2011, OPM Assistant Inspector General for Investigations Michelle B. Schmitz told a Senate hearing in June, shortly after Snowden's leaks were first published.
Sen. Claire McCaskill, D-Mo., who heads the Senate Homeland Security Subcommittee on Contracting Oversight, said Thursday she was outraged by the latest USIS revelation.
"From Edward Snowden to Aaron Alexis, what's emerging is a pattern of failure on the part of this company, and a failure of this entire system, that risks nothing less than our national security and the lives of Americans," McCaskill said in a statement.
"What's most frightening is that USIS performs a majority of background checks for our government," she said. "We clearly need a top-to-bottom overhaul of how we vet those who have access to our country's secrets and to our secure facilities. I plan to pursue such an overhaul."
Security clearance and background investigations for OPM cost taxpayers about $1 billion last year, an expense expected to rise to $1.2 billion by 2014, McCaskill's office said.