Thomas Edward Caldwell, leader of a far-right militia group, is being investigated by the FBI.
He is accused of coordinating an effort to locate lawmakers during the Capitol siege, an affidavit reveals.
Several Facebook messages gave specific directions as to the whereabouts of members of Congress.
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Thomas Edward Caldwell, leader of the far-right militia group Oath Keepers, has been accused by the Federal Bureau of Investigation of coordinating an effort to track down lawmakers during the siege of the US Capitol building.
Caldwell, 66, is cited with leading the effort to locate members of Congress, according to The Washington Post.
Two others, Donovan Ray Crowl and Jessica Marie Watkins, are also accused of having conspired with the Navy veteran, The Post reported.
Caldwell is said to have received Facebook messages updating him of the specific whereabouts of lawmakers while congressional offices were being ransacked, according to a sworn affidavit included in court filings obtained by the George Washington University Program on Extremism.
Read more: I went inside the US Capitol's immense security bubble to cover the most surreal presidential inauguration of my lifetime. Here's what I saw.
One message, the FBI said, read: "All members are in the tunnels under capitol. Seal them in, turn on the gas."
While raiding the Capitol, Caldwell shared a post on Facebook. He simply wrote: "Inside." After this, the intelligence agency said that he received a flurry of messages from unspecified senders.
"Tom take that b**** over," read one message.
"Tom, all legislators are down in the Tunnels 3 floors down," said another.
Some of the messages gave very specific directions about the locations of lawmakers. "Go through back house chamber doors facing N left down hallway down steps," court documents reveal of one message.
"Do like we had to do when I was in the core, start tearing out floors, go from top to bottom," another is reported to have said.
The day after the insurrection, Caldwell sent a text to Crowl. It read: "Do you like the pictures of us storming the castle?"
Caldwell was arrested earlier this week on several charges, including conspiracy to commit an offense against the United States and conspiracy to impede or injure an officer.
It was the first conspiracy charge filed against any of the rioters, according to the Daily Beast.
The investigation into the insurrection is underway but Rep. Alexandria Ocasio-Cortez has said that "a very considerable amount" of lawmakers "still don't feel safe."