Any members of the U.S. Congress who helped a crowd of President Donald Trump's supporters storm the Capitol should face criminal prosecution, House of Representatives Speaker Nancy Pelosi said on Friday.

The unprecedented January 6 attack on the seat of Congress left five dead and led the House to impeach Trump a second time for a fiery speech that day in which he urged thousands of his followers to fight Democratic President-elect Joe Biden's victory.

The hundreds who stormed the Capitol quickly overwhelmed police guarding the building, calling security preparations into question, and showed a level of detailed knowledge about the location of lawmakers' offices by some rioters that raised suspicions.

Democratic Representative Mikie Sherrill, a former U.S. Navy helicopter pilot, has accused some Republican lawmakers of helping Trump supporters, saying she saw colleagues leading groups on "reconnaissance" tours on January 5.

Pelosi was asked at a news conference whether any actions would be taken against lawmakers who may have brought tours to the Capitol the day before the attack, which briefly halted Congress in its duty of certifying Biden's win.

"If in fact it is found that members of Congress were accomplices to this insurrection, if they aided and abetted the crimes, there may have to be actions taken beyond the Congress, in terms of prosecution for that," Pelosi said.

The Capitol Police is investigating whether members of Congress led people through the Capitol the day before the attack. "The matter is under investigation," said Capitol Police spokeswoman Eva Malecki.

More than 30 House Democrats, including Sherrill, have asked the acting House and Senate sergeants-at-arms and the acting head of the Capitol Police for information about who was in the building on January 5.

Pelosi announced a security review of the siege by Trump followers, some of whom were aligned with white supremacist groups. The review would study the Capitol's security infrastructure, procedures, and "command and control," she said.

Some Republican Representatives have loudly protested security measures put in place since the attack, including new requirements that everyone entering the House chamber pass through a metal detector.

The march by Trump's supporters had been publicized for weeks. There was no direct evidence to suggest rioters had formed "kill capture teams," the top federal prosecutor in Washington, D.C. said on Friday, softening a statement made by U.S. prosecutors in Arizona in a court filing late on Thursday.

The U.S. Justice Department's internal watchdog will review how the FBI and other law enforcement agencies prepared and responded, Inspector General Michael Horowitz said on Friday.

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No timeline for Senate trial

The House on Wednesday approved an article of impeachment charging Trump with incitement of insurrection for his speech immediately before the attack.

Pelosi declined to answer questions from reporters about when she would send the article to the Senate, the step necessary to trigger a trial. A spokesman for the speaker said he could not confirm a CNN report later on Friday that she is expected to send the article next week.

Trump is not expected to face trial before his term ends on January 20, though lawmakers could bar him from running for office again.

Congressional Democrats have been grappling with how to balance the impeachment of Trump with other Senate priorities including confirming Cabinet nominees and addressing Biden's request for a $1.9 trillion coronavirus relief package.

When Biden takes office on Wednesday, he will be leading a nation in which more than 388,000 people have died of COVID-19, which is infecting more than 235,000 people per day.

"This is a matter of complete urgency," Pelosi said of COVID-19 vaccine distribution under Biden's proposal.

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According to Senate rules, the trial would start the day after the charge is sent over by the House. The last time the House voted to impeach Trump, in December 2019, Pelosi did not transmit the charges to the Senate for weeks.

Those charges related to abuse of power and obstruction of Congress stemming from Trump's request that Ukraine investigate Biden and his son Hunter. The Senate in February 2020 voted to acquit Trump, keeping him in office.

Democrats said on Friday they are bringing back two outside lawyers who helped prosecute Trump's first impeachment: Barry Berke, who will serve as chief impeachment counsel, and Joshua Matz, according to a House Judiciary Committee statement.

The Senate is scheduled to return to Washington on Tuesday, the day before Biden's inauguration.

A presidential inauguration traditionally draws hundreds of thousands of visitors, but the ceremonies had been scaled back dramatically because of the COVID-19 pandemic, even before last week's riot.

Now Washington is wrapped in a security blanket with thousands of troops and law enforcement officers on duty.

Farewell to the White House

Trump now plans to leave Washington on the morning of Inauguration Day next Wednesday after considering a departure on Tuesday, two sources familiar with the matter said on Friday.

Trump, who had already said he will not attend Biden's inauguration, is planning a ceremonial farewell at Joint Base Andrews, the base outside Washington where Air Force One is headquartered, the sources said.

The farewell could include a 21-gun salute, one source said. The sources stressed that the plan could change. It was unclear whether he would speak on Wednesday.

Trump will then fly on to Palm Beach, Florida, to begin his post-presidency at his Mar-a-Lago club, according to the sources. He is likely to be in Florida by the time Biden is inaugurated at midday on Wednesday.

A handful of White House aides plan to work for Trump in Palm Beach as the former real estate tycoon works on retaining his clout in the Republican Party.

Some advisers have been urging the president to host Biden for a White House meeting ahead of Inauguration Day, but there has been no sign Trump is willing to do that, an administration official said.

(With input from Reuters)