Lawmakers from both parties are demanding investigations into how a mob of President Donald Trump supporters managed to overwhelm security at the U.S. Capitol, including whether they got any assistance from inside the building.

A new, fortified perimeter has been erected around the Capitol grounds in anticipation of the potential for more violence during the inauguration of President-elect Joe Biden on Jan. 20. While physical security has been heightened, members of Congress are still waiting for answers about what went wrong.

Representative Brian Fitzpatrick, a Pennsylvania Republican and a former FBI agent, said allegations that rioters had help inside the Capitol will be subject to a nationwide investigation by the bureau.

“This is going to be a very broad, wide-ranging investigation, and it should be, because what happened last week was a major catastrophe,” Fitzpatrick said. “Part of their job is to make sure everyone who participated is held accountable and to make sure it never happens again.”

The crowd was in Washington for a rally promoted by Trump, who has made baseless claims about voter fraud and refused to recognize Biden as the winner of November’s election. The president told his supporters on Jan. 6 to “fight like hell“ and urged them to march on the Capitol, where violence quickly escalated. The mob broke through doors and ransacked some offices. A protester was killed by law enforcement and a police officer died after being injured in the riot. At least three other people died of medical emergencies.

Several Democrats are questioning the actions of some of their Republican colleagues and the Capitol Police force because the mob moved quickly through multiple stairways and hallways to find their way to the House and Senate chambers and various offices.

“Members of the group that attacked the Capitol seemed to have an unusually detailed knowledge of the layout of the Capitol Complex,” a group of more than 30 Democrats wrote in a letter asking the Capitol Police and acting sergeants at arms to investigate “suspicious behavior and access given to visitors” the day before the attack, despite limits placed on visitors because of the pandemic.

One of those Democrats, New Jersey Representative Mikie Sherrill, a former Navy pilot, has alleged without providing public evidence, that tour groups organized by member offices were doing “reconnaissance“ on Jan. 5.

The letter asked for Jan. 5 visitor logs and whether there was a way to ensure that “one staffer did not bring more than their allotted ‘official visitors’ through multiple entrances.”

Sherrill said her chief of staff reported the tour groups to the sergeant at arms on Jan. 5.

Requests for visit with lawmakers or constituent tours of the Capitol were often accommodated before visitation policies were tightened due to the coronavirus.

One Republican aide said several GOP offices were contacted by constituents and others who wanted to see the election overturned and were planning to attend the Jan. 6 rally. Some of these people asked to meet with lawmakers and wanted them join the protest, the aide said.

Republicans on the House Administration Committee introduced legislation this week to establish a commission, similar to the one after the Sept. 11, 2001 attack, to investigate what they called a “domestic terrorist attack.” The commission would consist of five Republicans and five Democrats.

There is a high level of concern among Democrats that some members of the Capitol Police and certain GOP lawmakers and staff may have helped coordinate parts of the attack, according to a Democratic aide. Many staff members say they longer feel safe coming into the Capitol, the aide said.

Representative Jamaal Bowman, a newly sworn-in Democrat from New York, also introduced legislation calling for an investigation of the role of Capitol Police and any connections with White supremacists.

There were officers who “seemed to be aiding and abetting insurrectionists as they attacked the Capitol,” he said in video posted on his Twitter. “We need to look at if there’s be an infiltration of Capitol Police.”

Separately, a spokesperson for Representative Ayanna Pressley, a Massachusetts Democrat, said panic buttons throughout her office were removed prior to the attack. The staff previously used the devices and were unaware they had been removed. The spokesperson said an investigation has been launched into the matter.