Stewart Rhodes of the Oath Keepers uses a radio as he departs a Trump rally in Minneapolis
Oath Keepers militia founder Stewart Rhodes uses a radio as he departs with volunteers from a rally held by U.S. President Donald Trump in Minneapolis, Minnesota, U.S. October 10, 2019. Reuters

An FBI agent will testify on Tuesday in the trial of the founder of the anti-government Oath Keepers group and four others accused of plotting to use force on Jan. 6, 2021, to stop Congress from certifying President Joe Biden's election victory.

FBI Special Agent Byron Cody will resume testifying about evidence the government gathered for the case, including a series of inflammatory texts, speeches and online posts by Oath Keepers founder Stewart Rhodes.

In those messages, Rhodes spoke about the potential for a "bloody" war and told followers that they needed to take matters into their own hands if former President Donald Trump failed to invoke the Insurrection Act, a 19th century U.S. law that empowers presidents to deploy troops to quell civil unrest.

Rhodes and his four co-defendants - Thomas Caldwell, Kenneth Harrelson, Kelly Meggs and Jessica Watkins - are accused of conspiring to try to keep Republican Trump in power after he had lost the 2020 election. A pro-Trump mob charged into the U.S. Capitol on Jan. 6 and attacked police, but failed to prevent lawmakers from certifying Biden's victory.

Seditious conspiracy is a rarely prosecuted crime under a statute dating to the Civil War era and is defined as attempting "to overthrow, put down or to destroy by force the government of the United States." It carries a possible prison sentence of 20 years.

Prosecutors have said some of the Oath Keepers were among the Trump supporters who stormed the Capitol building after he gave a speech repeating his false claims that the election had been stolen from him through widespread voting fraud. Five people died during and shortly after the riot and about 140 police officers were injured.

In addition, prosecutors have said the Oath Keepers organized a "quick reaction force" of armed members who were kept on standby across the Potomac River in Virginia in case they were called upon to bring firearms into Washington.

Prosecutors this week are expected to call two more FBI agents to testify in the trial, as well as Ernest Hancock, an Arizona-based podcaster.

According to court filings, Hancock interviewed Edward Vallejo, an Oath Keeper and alleged co-conspirator who goes on trial in November and who is accused of helping coordinate the quick reaction force that was staged in Virginia.

In the interview, Vallejo told Hancock that if Congress certified Biden's election, then "that's going to be the declaration of a guerilla war."

Attorneys for the defendants have said the evidence will show they did nothing illegal and that the Oath Keepers are a peacekeeping group that has done security work at events around the country to protect speakers at political rallies.

Rhodes is expected to take the stand in his own defense later in the trial.