The government contractor responsible for checking Navy Yard shooter Aaron Alexis' background before he could gain security clearance several years ago did not attempt to obtain a police report that would have shown he had "anger management problems," a top U.S. official acknowledged Thursday.

The police report detailed an incident in Seattle, in which Alexis used a pistol to shoot out his neighbor's tires during what he told police was a blackout fueled by anger.

In a Senate committee hearing looking at government clearances and the Navy Yard shooting Sept. 16, Office of Personnel Management Acting Director Elaine Kaplan testified that when the government contractor, USIS, conducted Alexis' background investigation in 2007 as part of his application to join the U.S. Navy, they consulted an FBI database and found that Alexis had been arrested three years earlier.

Based on past experience with Seattle law enforcement, USIS assumed that they would not be able to obtain the full police report, instead turning to a Washington state database offering only generic information, Kaplan told lawmakers.

Republicans and Democrats both called that move "shocking."

Sen. Kelly Ayotte, R-N.H., a former prosecutor, said the background investigator should have pursued the full police report because "getting a police report would have flagged a very different set of conduct."

The government seems to believe, "Well, if a police department won't give us a report, we've checked the box," suggested Sen. Claire McCaskill, D-Mo, taking direct aim at Kaplan, the OPM official.

"Now, I get it that we can't go out and do one-on-one on every application for clearance," McCaskill said. "But the notion that you're calling what you're doing quality control, Ms. Kaplan, is probably, I think, offensive."

Though many are questioning USIS's decision not to obtain the police report, Kaplan insisted USIS followed protocol.

"Yes, we all missed something, to be sure, but we did what was required," Kaplan testified. "We conducted the investigation that was required by the investigative standards. … Should we be required to get police reports, for example? Should we be required to get mental health information even from someone who has a secret as opposed to a top secret clearance? All these things need to be looked at. But it was not, in our view, a case of malfeasance … We believe the contractor did what they were supposed to do."

USIS conducted the background investigation on Alexis for the Office of Personnel Management, a common practice. The background check turned up the 2004 gun incident in Seattle, but instead of referencing any shots fired a car's tires, the OPM summary only mentioned that Alexis "retaliated by deflating the male person's tires."

In conducting its background check on Alexis, USIS never attempted to obtain the police report, according to Kaplan. She said USIS assumed it was a lost cause because Seattle police routinely referred them to a state database, which contains only limited information about a case. That database indicated charges had been dropped.

The revelation that USIS failed to pursue Alexis' police record came on the heels of a Justice Department announcement that USIS - the same firm that vetted National Security Agency leaker Edward Snowden - allegedly failed to perform mandated quality control reviews and is being sued under the False Claims Act. The suit, originally filed in 2011, was unsealed Wednesday.

Following the allegations, USIS appointed a new CEO and developed an internal audit committee, Kaplan said. OPM has also ramped up its own quality control efforts, increasing the frequency of on-site inspections and case audits. USIS continues to perform about 45 percent of OPM's background investigation, Kaplan told senators.

"A lot of changes have been made at USIS," Kaplan said. "That has given us some level of comfort and confidence that we can rely on these products. Rely but verify."

Several senators present at the hearing expressed concern not only about OPM's use of subcontractors like USIS, but their reliance on self-reporting - especially because Aaron Alexis lied about previous arrests when he applied for clearance.

When asked by a background investigator about the 2004 incident, Alexis said the person whose tires he had deflated had not pressed charges. He also told the investigator he would do things differently in the future and avoid confrontation.

"There need to be serious consequences for lying," McCaskill said. "This process has become a pro forma process."

During his years in the Navy from 2007 to 2010, Alexis had a number of run-ins with leadership, including after an arrest for disorderly conduct in Dekalb County, Ga. He was also arrested in September 2010 in Fort Worth, Tex., after discharging his weapon in his apartment. Three months later, Alexis requested an early separation from the Navy, which was granted within days.

He ultimately started working as a private contractor, and by September of this year he was assigned to update computer systems inside the Navy Yard. That gave him access to the building, where he gunned down 12 people during a vicious rampage.

-ABC News' Luis Martinez contributed to this report