Secret Service Director Julia Pierson will face questions about how an armed intruder jumped the White House fence and made it as far as the East Room when she testifies before a House committee on Tuesday. 

Sources confirmed to Fox News on Monday that 42-year-old Omar Gonzalez overpowered a Secret Service officer in the Sept. 19 incident -- this led to a struggle and "wrestling" inside the executive mansion as he darted through. Gonzalez was eventually tackled by a counter-assault agent in the East Room after he reached the doorway to the Green Room, a parlor overlooking the South Lawn. 

The revelation that the intruder made it much farther than originally known came on the eve of a scheduled House Oversight and Government Reform Committee hearing that will address the breach, as well as lawmakers' "concerns" about the Secret Service's security protocols. 

A series of what one source called "catastrophic" security failures apparently allowed the intruder to get deep into the White House. 

The Secret Service did not follow basic protocols during the incident to protect the White House, the president and the first family and the agency still does not know why, a source intimately familiar with details of the investigation told Fox News. 

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For example, the Secret Service didn't lock down certain areas of the property and did not elevate the threat level at the White House so that other uniformed officers and agents would know what was happening, which is a standard response.

“This was a catastrophic failure when the President was not there. What if the president was there?” the source, a longtime Secret Service insider, added. "It turns out that basic functions in place to avoid this were never initiated." 

Rep. Jason Chaffetz, R-Utah, who chairs a House subcommittee on national security oversight, also told CNN that whistleblowers had informed his panel of the breach. 

Additionally, an alarm box near the front entrance of the White House that is designed to alert guards to an intruder had been muted at what officers believed was a request of the usher's office, an official told The Washington Post.

An officer posted inside the front door also appeared to be delayed in learning that Gonzalez was about to burst through, according to the Post. Officers are trained to immediately lock the front door once an intruder is spotted on the grounds.

A Secret Service Uniformed Division officer then “misreported” how far the intruder got into the White House to management in order to downplay the impact of the initial failure. 

The officer in question told management that the intruder “never got through the vestibule” of the North Portico, which turned out to be false, a source said.

Secret Service spokeswoman Nicole Mainor told Fox News that the agency would not comment on the revelations, citing the ongoing investigation.

The Secret Service has been having high-level meetings to address the breach, the latest in a series of embarrassing scandals for the agency since a 2012 prostitution scandal erupted during a presidential visit to Colombia.

The Post reported over the weekend that the Secret Service did not immediately respond to shots fired at the White House in 2011, amid what the agency describes as uncertainty about where the shots originated. Four days later, it was discovered that at least one of the shots broke the glass of a window on the third level of the mansion, the Secret Service said.

At the time of the 2011 breach, the president and first lady Michelle Obama were away, but their daughters were in Washington — one home and the other due to return that night.

Oscar R. Ortega-Hernandez of Idaho has been sentenced to 25 years in prison for the 2011 incident.

"The president and the first lady, like all parents, are concerned about the safety of their children, but the president and first lady also have confidence in the men and women of the Secret Service to do a very important job, which is to protect the first family, to protect the White House, but also protect the ability of tourists and members of the public to conduct their business or even tour the White House," White House spokesman Josh Earnest said Monday.

After the most recent breach, Pierson ordered a review of the incident and possible changes to security measures at and around the White House. She briefed the president on Thursday.

"The president is interested in the review that they are conducting, and I would anticipate that he'll review whatever it is they — whatever reforms and recommendations they settle upon," Earnest said of the Secret Service's internal review.

Secret Service officers who spotted Gonzalez scaling the fence quickly assessed that he didn't have any weapons in his hands and wasn't wearing clothing that could conceal substantial quantities of explosives, a primary reason agents did not fire their weapons, according to a U.S. official briefed on the investigation.

Gonzalez was on the Secret Service radar as early as July when state troopers arrested him during a traffic stop in southwest Virginia. State troopers there said Gonzalez had an illegal sawed-off shotgun and a map of Washington tucked inside a Bible with a circle around the White House, other monuments and campgrounds. The troopers seized a stash of other weapons and ammunition found during a search of Gonzalez's car after his arrest.

The Secret Service interviewed Gonzalez in July, but had nothing with which to hold him. Gonzalez was released on bail. Then, on Aug. 25, Gonzalez was stopped and questioned again while he was walking along the south fence of the White House. He had a hatchet, but no firearms. His car was searched, but he was not arrested.

"There's a misperception out there that we have some broad detention powers," Ed Donovan, a Secret Service spokesman, said. The Secret Service, like other law enforcement agencies, must have evidence of criminal behavior in order to file charges against someone. "Just because we have a concern about someone doesn't mean we can interview or arrest them or put them in a mental health facility," Donovan said.

Click here for more from the Washington Post.

Fox News' Ed Henry, Lesa Jansen, Mike Emanuel, Chad Pergram and Wes Barrett and The Associated Press contributed to this report.