Contractor that vetted Snowden says it ran background check for Navy Yard shooter USIS spokesman Ray Howell said the company got new information Thursday. "Today we were informed that in 2007, USIS conducted a background check of Aaron Alexis" for the Office of Personnel Management, Howell said in a statement. 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, which was spun off from the federal government in the 1990s, has become the largest private provider of government background checks. With 7,000 employees, the company handles about 45 percent of all background checks for the OPM, congressional staffers say. Despite the investigation, there was no indication that USIS did anything improper when it vetted Alexis. A statement late Thursday by the OPM division that handles security checks for most federal agencies said that the 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." The statement by Merton W. Miller, associate director of OPM's Federal Investigative Services, acknowledged that Alexis's background investigation was carried out "with support from a Government contractor, USIS." "OPM's involvement with matters related to Aaron Alexis" security clearance ended when we submitted the case to the Department of Defense . . . for adjudication in December 2007," Miller's statement said. The DOD "did not ask OPM for any additional investigative actions after it received the completed background investigation." Government officials said this week that the 2007 background check uncovered an incident in which Alexis shot out the tires of a car. The 2004 incident was characterized as "malicious mischief." Two other run-ins with law enforcement and reports of more serious mental-health issues occurred years after the initial background check. Lower-level clearances such as the one granted to Alexis typically remain valid for a decade. The government's security clearance process is not designed to flag people struggling with mental illness, experts said. The aim of the system is to root out individuals at risk of compromising classified information. Mental-health treatment is not a disqualifying factor, and there are few ways to alert security officials when someone with clearance develops mental-health problems, according to analysts and former government security officials. Federal officials are trying to implement a system that would continuously evaluate personnel with classified security clearance. But with nearly 5 million federal workers holding secret or top-secret security clearance, government officials say they are struggling to keep track of all their cases. Tom Hamburger contributed to this report.