Watch: Secret Service Can't Answer Key Trey Gowdy Questions on 2011 White House Shooting

Secret Service Director Julia Pierson on Tuesday indicated her agency had little or no reason to decide that the shots fired at the White House in 2011 was just the noise of a car backfiring, and failed to answer why agents didn't do a thorough examine of the White House grounds after the shooting.

Pierson was pressed on the 2011 shooting by Rep. Trey Gowdy (R-S.C.) at a House Oversight hearing, which also dealt with this month's incident in which a fence-jumper was able to enter the White House and enter several rooms before being taken out.

On the 2011 shooting, Gowdy noted that several Secret Service agents said they smelled gunpowder and drew their weapons in response to what they thought was a shooting. But after a brief examination, the Secret Service decided, in coordination with the U.S. Park Service, that the noise of the shots were just a car backfiring.

Gowdy started by asking why agents didn't run through a full examination of the White House, even if some believed it might have been a car backfiring.

"Even if that were true, given the very small investment of resources, why not investigate the shots fired?" Gowdy asked. He said the failure of the agency to do a full investigation allowed a housekeeper to find evidence of the shooting in the residence area of the White House a few days later.

"The housekeeper was able to locate fragments of glass on the Truman balcony, which is not an area that is frequented by security personnel," Pierson explained. But Gowdy said that only shows the Secret Service didn't do a full examination of the building.

When asked again by Gowdy what evidence they had of a car backfiring, Pierson actually made the opposite point, by saying witnesses said they saw a shooter on Constitution Avenue. Finally, she admitted she doesn't know what led agents to decide it was a car backfiring.

"I can't speak to the specificity of the individual you're talking about who reported it…" she said.

Gowdy pressed again on why agents wouldn't do a thorough search of the grounds right away. But her only answer was the initial sweep wasn't good enough.

"The initial shooting incident occurred at 9:30 at night," she said. "It's difficult to see at night. Officers heard the shots fired on Constitution Avenue. Officers reacted, picked up security positions, swept the area looking for any type of injury, any type of intruder."

"It is my understanding that a perimeter sweep was done. Was it as thorough as it needed to be? Obviously not," she said.