Federal contractors who conducted a background check on Aaron Alexis when he enlisted in the military knew that he falsely reported that he had never been arrested or charged with any firearms offenses but he nevertheless was granted a security clearance, Navy officials disclosed Monday.

The contractors who conducted the check when Alexis applied to join the Navy in 2007 discovered that he had been arrested in Seattle three years earlier. But in a report to the Navy, the investigators minimized the incident and left out the most alarming allegation — that Alexis had been charged with shooting out someone’s car tires after an argument, according to documents released by the Navy.

The disclosure is further evidence of how Alexis’s violent and erratic behavior was overlooked or dismissed over several years, a period that culminated Sept. 16, when he erupted in a rampage at the Navy Yard, killing 12 people.

Alexis’s security clearance background check was performed by USIS, a Falls Church government contractor, on behalf of the federal Office of Personnel Management. Last week, OPM said in a statement that the check was performed properly, “in compliance with all investigative standards.”

Portions of the check provided to the Navy, however, do not mention that he had been charged with a gun-related crime in Seattle, only that he had been engaged in a verbal altercation with a construction worker. Navy officials said they never received police reports or court records detailing the case.

The documents show that background-check investigators interviewed Alexis — but no one else — about the incident and that he played down its seriousness. Alexis said the reason he did not disclose the arrest on his security clearance application was that the charge had been dismissed and he thought it had been erased from his record.

After the background check was completed, the Navy granted Alexis a security clearance in March 2008. He retained the clearance after he left the Navy in 2011, enabling him to continue to work at military installations as a defense contractor.

A senior Navy official told reporters Monday that there is “no way to know objectively” whether the Navy would have approved Alexis’s security clearance had it known about his gun-related arrest. The official said he did not know whether lying on a security clearance application should have been automatic grounds for rejection. He spoke on the condition of anonymity under rules set by the Navy.

Ray Howell, a spokesman for USIS, said his firm is contractually prohibited from retaining background-check case files, so it could not comment on the Navy’s version of events.

Seattle police have said that they were preparing to charge Alexis with a felony in 2004 but that the charges were later knocked down to a misdemeanor. Authorities ultimately lost the paperwork, and the case was dropped — even though Alexis had confessed to the crime.