“Certainly if you have an organised armed assault on the Capitol, or any government installation, it’s absolutely a charge that can be brought,” said Andrew McCarthy, a former federal prosecutor who secured convictions at Abdel-Rahman’s 1995 trial.

The challenge, he said, is whether prosecutors can prove people conspired to use force.

“In our case, conspiracy was a lay-up because of the nature of the terrorist cell we were targeting. In this case, can they show conspiratorial activity or was it one of these things that spontaneously combusted, which makes conspiracy harder to prove?” McCarthy said.

Karen Greenberg, director of the Center on National Security at the Fordham University School of Law, said sedition charges in an attack against the centre of US government are even more appropriate than in the New York bombing plot.

“Of course we should use it here. That’s what this is, seditious conspiracy,” she said.

Prosecutors had scant evidence against Abdel-Rahman when they arrested him months after a bomb exploded in February 1993 at the World Trade Centre, killing six people.

Then-Manhattan U.S. Attorney Mary Jo White went to Washington to convince the FBI and Attorney General Janet Reno that Abdel-Rahman should be charged with seditious conspiracy, a law enacted after the Civil War to arrest Southerners who might keep fighting the U.S. government.

The law’s hefty penalty — up to 20 years — boosted its value before terrorism laws were overhauled in 1996, McCarthy said.

Prosecutors offered jurors Abdel-Rahman’s fiery speeches, witness testimony and a recording of his conversation with an FBI informant in which the sheikh said US military installations could be attacked.

Abdel-Rahman argued on appeal that he was never involved in planning actual attacks against the U.S. and his hostile rhetoric was protected free speech. His conviction was upheld and the so-called “Blind Sheikh” died in prison in 2017 aged 78.

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In another case, Oscar Lopez Rivera — a former leader of a Puerto Rican independence group that orchestrated a bombing campaign that left dozens of people dead or maimed in the 1970s and 1980s — spent 35 years in prison for seditious conspiracy before President Barack Obama commuted his sentence in 2017.

In 2012, US District Judge Victoria A. Roberts in Detroit dismissed seditious conspiracy charges brought against a militia group’s members who spoke of engaging local, state and federal law enforcement in combat.

While considering bail in the case, the judge said “their right to engage in hate-filled, venomous speech is a right that deserves First Amendment protection.” She also wrote that the group’s rhetoric spoke of “reclaiming America, not overthrowing the United States Government.”

Before the Capitol attack, federal prosecutors talked about using the seditious conspiracy statute in cases involving protests against police brutality, though none were brought.

In a September 17 memorandum, Jeffrey A. Rosen, now the acting U.S. Attorney General, urged prosecutors nationwide to consider filing seditious conspiracy charges against what he called “violent rioters” during racial injustice demonstrations sparked by the police killing of George Floyd.

Rosen wrote that the law didn’t require proof of a plot to overthrow the US government.

Lawyers interviewed by The Associated Press agreed that it would be stretch to try to put President Donald Trump or lawyer Rudolph Giuliani on trial for sedition for what some have criticised as incendiary rhetoric at the rally preceding the mob attack on the Capitol.

McCarthy labelled Trump’s actions that day reprehensible, but said “you would never be able to prove beyond a reasonable doubt that he intended force to be used”.

Carl Tobias, a University of Richmond law professor, said prosecuting Trump for urging people to march to the Capitol and not be “weak” or other statements would be a problem.

“I think people who work in the area of criminal procedure would say it has a checkered history,” Tobias said of seditious conspiracy law, which has drawn criticism for targeting those with unpopular views and chilling free speech.

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“People who are absolutists about the First Amendment would be troubled by it and civil libertarians on either end of the spectrum,” he said.

New York civil rights lawyer Ron Kuby, who represented Abdel-Rahman for a time, predicted that with or without a sedition charge, the people who committed the most serious offences at the Capitol will pay “a substantial price, certainly a price none of them ever expected”.

“Those who started a riot have no idea just how oppressive the government can actually be and they are about to find out,” Kuby said.