US Secret Service director Julia Pierson testifies at the House Oversight and Government Reform Committee hearing on Capitol Hill in Washington September 30, 2014. (Photo: Reuters)

Updated Oct. 1: Secret Service Director Julia Pierson, the first female director of secret service, has resigned on Wednesday, Homeland Security Director Jeh Johnson announced the resignation in a statement. President Obama has accepted the resignation. 

Congress is demanding answers from the Secret Service about a security breach at the White House on Sept. 19, where an Army veteran managed to jump over the fence of the White House and went as far as the East Room before being tackled by an off-duty agent.

The Secret Service initially reported in a court filing that the veteran, Omar Gonzalez, supposedly jumped the White House fence and made it all the way to the front doors, which were unlocked. The federal agency also decided to mute an alarm system to avoid disturbing people in the White House. However, CNN reports that a law enforcement official said that the intruder actually made it to the East Room.

Secret Service Director Julia Pierson faced tough questions from the House Oversight and Government Reform Committee yesterday about the incident. Lawmakers from the House want to conduct a thorough probe of the agency through a team of independent investigators.

"It's clear that our security plan was not executed properly. I take full responsibility. What happened is unacceptable and it will never happen again," Pierson said in her opening remarks.

Rep. Darrell Issa, R-Calif., grilled Pierson on the Secret Service's personnel budget.

"Eight hundred million dollars a year...during your tenure...and that door was unlocked," Issa said.

"The door was unlocked at the time of Mr. Gonzalez's entry, that's correct," Pierson said, later noting that the front doors of the White House now have automatic locks.

Issa, the chairman of the committee, thought the security breach was unacceptable.

"An intruder walked in the front door of the White House. That is amazing - and unacceptable. Common sense tells us this was a significant security failure - not an instance of praiseworthy restraint," Issa said.

According to the Wall Street Journal, the explanations provided by Pierson about the incident left those in the committee unsatisfied. Although she faced more than three hours of questions from House lawmakers on Tuesday, she did not mention anything related to a security breach that happened several days before that incident.

Rep. Jason Chaffetz, R-Utah, brought up information that President Obama rode in an elevator at the Centers for Disease Control and Prevention in Atlanta on Sept. 16 with an armed contract security guard convicted of felonies. In most cases, convicted felons are not allowed to carry guns.

"This person was within arm's length of the president with a gun. He has three felony convictions for assault and battery is my understanding. He was never given a background check. He was not badged by the Secret Service," Chaffetz said.

According to the Washington Post, Chaffetz later called on Pierson to resign from her post, saying that "things have gotten worse, not better, under her tenure."

Pierson, who has worked at the Secret Service for 30 years, became the head of that federal agency last year and largely focused on strengthening its disciplinary procedures and restoring its reputation.

It remains unclear on whether or not Pierson herself knew about the Sept. 16 incident.