A man authorities say is a leader of the far-right Oath Keepers militia group and led other extremists in the attack on the U.S. Capitol discussed the possibility of getting a boat to ferry "heavy weapons" across the Potomac River, prosecutors said Thursday.

Court papers filed in the case against Thomas Caldwell provide chilling new evidence in the plot on Capitol Hill as Democrats prosecuting Donald Trump's impeachment made their case to convict the former president for inciting the violence.

The details come days after Caldwell's lawyer said the man — who authorities said holds a leadership position in the extremist group — had a top-secret security clearance for decades and previously worked for the FBI. The FBI has not answered questions about the lawyer's claim and Caldwell's lawyer has not responded to multiple messages.

Prosecutors said Caldwell sent a text message to someone believed to be affiliated with the Three Percenters, an anti-government movement, on Jan. 3 about the possibility of sending weapons across the river.

"How many people either in the militia or not (who are still supportive of our efforts to save the Republic) have a boat on a trailer that could handle a Potomac crossing?" Caldwell wrote, according to prosecutors. "If we had someone standing by at a dock ramp (one near the Pentagon for sure) we could have our Quick Response Team with the heavy weapons standing by, quickly load them and ferry them across the river to our waiting arms."

Prosecutors revealed the evidence to make the case that Caldwell should remain locked up while he awaits trial.

Authorities also said that during a search of Caldwell's home, they also found a "Death List" that included the name of an elected official from another state. Investigators also found invoices for more than $750 worth of live ammunition and what appeared to be a gun designed to look like a cellphone, prosecutors said.

Caldwell's lawyer is urging the judge to release him, saying he denies being a member of the Oath Keepers or ever going into the Capitol building. Defense Attorney Thomas Thomas Plofchan said Caldwell has held a top-secret security clearance since 1979, which required multiple special background investigations. Caldwell also ran a consulting firm that did classified work for the U.S. government, the lawyer said.

The Virginia man is among more than 200 people charged with federal crimes so far in the deadly siege. He was charged with conspiracy last month alongside two other accused members of the Oath Keepers, who are accused of planning in advance to carry out violence. Authorities say Caldwell began plotting to undo President Joe Biden's victory as early as the days after the election.

Prosecutors said the Oath Keepers communicated during the attack about the location of lawmakers. At one point during the siege, Caldwell received a message that said "all members are in the tunnels under the capital," according to court documents. "Seal them in turn on gas," it said.

Jessica Watkins, who authorities say conspired with Caldwell, indicated as Biden's inauguration approached that she "was awaiting direction from President Trump," prosecutors said in another court filing Thursday.

"I am concerned this is an elaborate trap," Watkins in a text message days after the election, according to the court papers. "Unless the POTUS himself activates us, it's not legit. The POTUS has the right to activate units too. If Trump asks me to come, I will."

There was no attorney listed for Watkins in the court record.