Accusing unnamed pro-Trump Republican colleagues of giving "reconnaissance" tours to some of the right-wing rioters who took part in the deadly January 6 mob attack on the U.S. Capitol, Rep. Mikie Sherrill on Wednesday led House Democrats in demanding a probe of GOP lawmakers' actions. 

In a letter to the head of the Capitol Police and the sergeants-at-arms for the House and Senate, Sherrill (D-N.J.) requested an "immediate investigation into the suspicious behavior and access given to visitors to the Capitol" on the day before it was stormed. 

"Many of the members who signed this letter, including those of us who have served in the military and are trained to recognize suspicious activity, as well as various members of our staff, witnessed an extremely high number of outside groups in the complex on Tuesday," Sherrill wrote. "This is unusual for several reasons, including the fact that access to the Capitol... has been restricted since public tours ended in March of last year due to the pandemic."

"The visitors encountered by some of the members of Congress on this letter appeared to be associated with the rally at the White House the following day," Sherrill added. "Members of the group that attacked the Capitol seemed to have an unusually detailed knowledge of the layout of the Capitol complex. The presence of these groups... was indeed suspicious."

Over 30 of Sherrill's Democratic colleagues signed the letter, which came amid reports of a claim by Sarah Groh, chief of staff for Rep. Ayanna Pressley (D-Mass.), that "every panic button" in the congresswoman's office was "torn out" ahead of the riot. Rep. Jamaal Bowman (D-N.Y.) also said that his office did not have a panic button, although he noted that he had only been a member of Congress for three days on January 6. 

The New York Times reported Wednesday that the inspector general of the Capitol Police is opening an investigation into January 6 security breaches and whether the department's officers were involved in the attack. So far, three Capitol Police officers have been suspended and 17 others are under investigation in connection with the riot. 

The Government Accountability Office (GAO), a nonpartisan federal watchdog agency, said it will also investigate what, if any, role members of Congress played in the insurrection. 

Rep. Jason Crow (D-Colo.), who requested the GAO inquiry, said that "to the extent there were members of the House that were complicit, and I believe there were, we will pursue appropriate remedies including expulsion and a prohibition from holding elective office for the rest of their lives."

Crow added that "they will of course be subject to criminal investigation and prosecution if that's what the facts of the investigation show."

Sherrill's letter follows a Tuesday Facebook Live video in which she accused "members of Congress who had groups coming through the Capitol" of leading future rioters as they conducted "reconnaissance for the next day."

"Those members who attempted to help our president undermine our democracy, I'm going to see that they're held accountable," Sherrill vowed in the video, adding that she planned to help ensure that Trump "is removed and never runs for office again and doesn't have access to classified material."

Although Sherrill did not name any of the Republicans she accused of leading the alleged reconnaissance tours, far-right Trump supporters including Reps. Andy Biggs (Az.), Mo Brooks (Ala.), and Paul Gosar (Az.) allegedly helped to organize the insurrection.

At least five people died during the attack, which occurred while lawmakers were attempting to certify the Electoral College vote that officially affirmed Biden as the next president.

Trump, along with some of his most prominent supporters, as well as numerous Republican members of Congress, stand accused of inciting the rioters with with lies about a "stolen election" and calls to "take back our country" and wage "trial by combat."

On Wednesday Sherrill joined her Democratic—and 10 GOP—colleagues in voting to impeach Trump, who became the first president ever to be impeached twice.