(CNN) Federal investigators are examining records of communications between members of Congress and the pro-Trump mob that attacked the US Capitol, as the investigation moves closer to exploring whether lawmakers wittingly or unwittingly helped the insurrectionists, according to a US official briefed on the matter.
The data gathered so far includes indications of contact with lawmakers in the days around January 6, as well as communications between alleged rioters discussing their associations with members of Congress, the official said.
The existence of such communications doesn't necessarily indicate wrongdoing by lawmakers and investigators aren't yet targeting members of Congress in the investigation, the official noted. Should investigators find probable cause that lawmakers or their staffs possibly aided the insurrectionists, they could seek warrants to obtain the content of the communications. There's no indication they've taken such a step at this point.
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With about 300 people facing charges, the investigation has shifted from the roundup of what law enforcement officials consider low-hanging fruit arrests of people accused of participating in the riot to those who allegedly conspired and planned the assault to disrupt the constitutional process of congressional certification of the election results.
Justice Department officials have assigned more than two dozen prosecutors, including some from outside Washington, to delve into more complex questions, including possible funding of insurrectionists and whether political figures, including lawmakers and staff, aided the attack, the US official said.
Law enforcement officials say one of the first steps taken after the insurrection was to seek cell phone tower data to try to identify people at the Capitol that day, a tactic allowed under existing law. That was necessary, the officials say, because among the multiple failures that day was the US Capitol Police allowing the hundreds of people who had attacked the building to leave without arrest.
Authorities announced only a handful of arrests on January 6, and the FBI and other agencies subsequently used a dragnet across the country to find the rioters.
Law enforcement officers have used what they call an "exclusion list." The list lets investigators see mobile devices that were authorized to be in the Capitol -- such as for Congress members and staff, law enforcement and other government and public safety officials -- while sifting out people who were not authorized to be in the building, according to a federal court filing in a riot-related case.
The FBI and Justice Department declined to comment.
FBI collection of phone metadata and geolocator data -- permissible under federal law -- was the subject of multiple lines of questions this week by some senators who pressed FBI Director Christopher Wray to reveal what investigators were doing with communications and financial data. Republican Sens. Mike Lee of Utah and Josh Hawley of Missouri suggested at a hearing Tuesday that the FBI could be overstepping its authority by scooping up communications data.
Investigators also have Capitol Police security footage that Democrats want examined to see if any members gave tours to riot participants in advance of January 6. Democrats have accused unnamed Republicans of providing rallygoers access, suggesting they were surveillance opportunities ahead of the riot.
Other lawmakers have a separate concern, that as investigators move closer to the activities of lawmakers, some members of Congress could use the protections of the Constitution's Speech or Debate Clause to try to block the work of the FBI. The clause provides legal immunity to members of Congress when carrying out their legislative duties.
Sen. Sheldon Whitehouse, a Rhode Island Democrat, says he's asked the Senate Ethics Committee to investigate because he believes Congress will be able to get information that the FBI may have trouble getting because of the Speech or Debate protections.
Whitehouse, in a telephone interview with CNN, says his effort is aimed at "making sure this isn't an investigation that is limited to the individuals who assaulted and entered the Capitol on January 6," adding that "potential culpability by members of Congress" has to be investigated.
The new phase of the federal probe is along the lines federal officials outlined after the attack. Acting US Attorney for the District of Columbia Michael Sherwin said that after the initial stage of rounding up rioters, prosecutors and investigators would begin examining more difficult aspects: including the funding and organizing of the riot, the likely interviews of lawmakers and even whether incitement at the rally held by President Donald Trump before the riot broke any laws. Prosecutors have also pushed to bring sedition charges against some alleged rioters, a step awaiting approval from the Justice Department, according to people briefed on the matter.
Sherwin has announced he will move to the Justice Department to help manage the cases for a period while the department sets out a longer-term plan for a sprawling probe that will stretch months.
Justice officials are mindful of the political and constitutional implications of parts of the investigation, particularly any that touch on members of Congress, according to law enforcement officials.
So far, investigators haven't found evidence that members of Congress knowingly aided or were involved in the insurrection, the US official said. The FBI has seized devices belonging to alleged rioters and has found communications that show connections that investigators plan to examine further.
In some cases, there is data showing past contact with lawmakers, and in others there's communications between alleged rioters discussing their associations with members of Congress. Some alleged rioters have also claimed to have provided security for lawmakers
In one case against an alleged leader of the right-wing paramilitary group the Oath Keepers, a defendant has claimed she was enlisted to provide security to legislators and others in their march to the Capitol.
None of this necessarily indicates wrongdoing by any lawmakers, the US official said.
At Tuesday's hearing, Wray said he couldn't provide details about specific steps the FBI has taken while the investigation is ongoing.
Asked by Hawley about the FBI's use of metadata and other information from cell phone towers, Wray said: "I feel confident that we are using various legal authorities to look at metadata."
Hawley, who helped lead the effort to block congressional certification of the election results during the riot, expressed frustration: "How are we going to know what you're doing with it and how are we going to evaluate the bureau's conduct if we don't know what authorities you're invoking, what precisely you're doing, what you're retaining?" Hawley said. "You're basically saying 'just trust us.'"