The riot at the U.S. Capitol on Jan. 6 was "a massive conspiracy," security analyst Juliette Kayyem told Boston Public Radio on Thursday.

After dozens of arrests, federal investigations are now building a case that the insurrection was planned and coordinated as an attack on the United States government, not a peaceful rally gone wrong.

"What's interesting is the FBI and the Department of Justice are returning to these charges in several cases and adding conspiracy charges," Kayyem said. "That would suggest, to someone like me who knows a lot about terrorism cases, that they are finding sufficient evidence of a nationwide conspiracy: funding, support, planning."

Kayyem said that, given the course of the investigations so far, she believes they will show that many people acted with criminal intent to attack the legislative branch.

"There was a suggestion in one of the pleadings that the Proud Boys, some of the defendants who are from the Proud Boys, may actually face terrorism charges," she said. "The U.S. attorney's office in those states reserve the right to amend the complaints to add terrorism charges."

Kayyem said she views the federal investigations into organizers of the Jan. 6 riot and Congress' impeachment of President Donald Trump as parallel tracks "with the same argument of the case."

"This was a conspiracy planned, organized, supported and incited by Donald Trump," she said, noting that federal criminal investigations have a much higher standard of proof than impeachment.

Kayyem said she wished Congress added another article of impeachment against Trump for what she called his "failure in his duty to protect," specifically former Vice President Mike Pence.

During a rally on Jan. 6., Trump stoked anger against fellow Republicans, including Pence, who didn't support his plan to subvert the election. Just a few hours later, Trump supporters surged into the Capitol chanting "hang Mike Pence."

"Regardless of if he knew what was going to happen or not, [that] seems impeachable in and of itself," Kayyem said.