White House intruder Omar Gonzalez was tackled by an off-duty Secret Service agent

WASHINGTON -- 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 Barack 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, past a stairway that leads up half a flight to the first family's living quarters, according to two people familiar with the incident.

No officers are assigned to guard the steps 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 condition of anonymity.

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 security on the northern fence line.

Though the Secret Service initially said that Gonzalez, who was carrying a knife, was quickly detained inside the front door, The Washington Post reported Monday that he actually made it well into the house before he was tackled on the far southern side of the 80-foot-long East Room.

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.

Pierson did not reveal during her testimony that the agent who tackled Gonzalez was off duty.