There were some heated moments Tuesday when Secret Service Director Julia Pierson testified before the House Oversight and Government Reform Committee about two security breaches at the White House, one in 2011 and one less than two weeks ago. (Sarah Parnass/The Washington Post)

There were some heated moments Tuesday when Secret Service Director Julia Pierson testified before the House Oversight and Government Reform Committee about two security breaches at the White House, one in 2011 and one less than two weeks ago. (Sarah Parnass/The Washington Post)

The man who jumped over the White House fence and sprinted through the main floor of the mansion could have gotten even farther had it not been for an off-duty Secret Service agent who was coincidentally in the house and leaving for the night.

The agent who finally tackled Omar Gonzalez had been serving on the security detail for President Obama’s daughters and had just seen the family depart via helicopter minutes earlier. He happened to be walking through the house when chaos broke out and the intruder dashed through the main foyer, according to two people familiar with the incident.

Gonzalez, 42, was the first person in modern memory to jump over the White House fence and get into the mansion, largely the result of a failure of numerous layers of Secret Service security on the northern fence line.

Though the Secret Service initially said that Gonzalez was quickly detained inside the front door, The Washington Post reported Monday that the man actually made it well into the house before he was tackled on the far southern side of the 80-foot-long East Room. Once he burst inside the unlocked front door, Gonzalez, an Army veteran, overpowered one Secret Service officer and, on his journey, sprinted past a stairway that leads up half a flight to the first family’s living quarters.

The additional information about the incident came as Secret Service Director Julia Pierson was being grilled on Capitol Hill about the Gonzalez incident and other security lapses revealed in Washington Post stories in recent days. The Post on Sunday detailed the agency’s fumbling response to a November 2011 shooting, in which a man fired a semiautomatic rifle into the White House residence while Sasha Obama was home, but the Secret Service discounted the gunshots on Constitution Avenue as a shoot-out between rival gangsters.

In the breach this past month, Gonzalez, who was carrying a knife, reached the doorway to the Green Room, a parlor overlooking the South Lawn with artwork and antique furniture, according to three people familiar with the incident.

Pierson confirmed in the hearing Thursday that, despite the Secret Service’s earlier assertion that Gonzalez was arrested inside the front door, Gonzalez was able to get far deeper into the White House and was eventually tackled outside the Green Room.

Lawmakers from both parties criticized Pierson and her agency for giving misleading and partial accounts of the security breach. The new information about the key role of an agent who happened to be in the building but was not part of the security team may raise further questions.

Pierson did not reveal during her testimony that the agent who tackled him was not actually assigned to the post where he confronted Gonzalez.

The agent, according to people familiar with the incident, who previously worked as a counter-assault team member, could easily have been outside or on his way home.

No officers are assigned to guard the steps to the Obama family’s private living quarters when the first family is not in the complex.

“There’s no telling how long this guy could have run around if the detail guy hadn’t happened to be there,” one person said on the condition of anonymity.