“This is the first step toward identifying and understanding that there was some type of concerted conspiracy here,” said one senior official with the U.S. Attorney’s Office for the District of Columbia, which is leading the investigation.

“Whether everyone else just happened to be there and got caught up in the moment, or if this is just the tip of the iceberg, how much this will grow at this point I can’t tell you, but we are continuing to investigate aggressively,” according to the official, who spoke on the condition of anonymity to discuss a pending investigation.

In charging papers, the FBI said that during the Capitol riot, Caldwell received Facebook messages from unspecified senders updating him of the location of lawmakers. When he posted a one-word message, “Inside,” he received exhortations and directions describing tunnels, doors and hallways, the FBI said.

Some messages, according to the FBI, included, “Tom all legislators are down in the Tunnels 3floors down,” and “Go through back house chamber doors facing N left down hallway down steps.” Another message read: “All members are in the tunnels under capital seal them in. Turn on gas,” the FBI added.