William Ayers, the former Weather Underground radical whose past made him a lightning rod in the 2008 presidential campaign, said Thursday that fired Colorado professor Ward Churchill became the victim of a "witch hunt" after comparing Sept. 11 victims to a Nazi.

"There's no doubt in my mind he was persecuted because of his politics," Ayers said before appearing with Churchill at a student rally on academic freedom at the University of Colorado at Boulder.

Churchill was a tenured professor of ethnic studies at Colorado University until he was fired on plagiarism charges in July 2007. He denies misconduct and is soon due to go to court in an attempt to get his job back.

In his lawsuit, he claims the university was looking for reasons to fire him because of his comments about the Sept. 11, 2001, terrorist attacks.

In an essay and a follow-up book, Churchill argued that the attacks were a response to a history of U.S. abuses. He said the victims of the World Trade Center collapse were "little Eichmanns," referring to Holocaust organizer Adolf Eichmann.

Churchill said Eichmann was a bureaucrat who carried out policies that were planned by others but was still responsible for his actions. The essay triggered a national firestorm and calls for his dismissal.

University spokesman Bronson Hilliard called Ayers' allegation "absolute nonsense." He said Churchill was fired because of proven research misconduct, not his statements.

Ayers was a co-founder of the Weather Underground, a radical anti-war group that claimed responsibility for a series of bombings, including explosions at the Pentagon and U.S. Capitol that didn't kill anyone.

He was a fugitive for years. After surrendering in 1980, charges against him were dropped because of prosecutorial misconduct.

Ayers is now an education professor at the University of Illinois-Chicago and an outspoken critic of intimidation of professors.

"Again and again, we have political leaders who weigh in on what's appropriate to teach and who's appropriate to teach," Ayers said Thursday.

He cited the University of Nebraska's decision to cancel his scheduled appearance at the Lincoln campus last fall after criticism from Nebraska Gov. Dave Heineman.

"Is that where we're heading, is the university a fiefdom of the governor? That's a little frightening," he said.

University officials have said they canceled Ayers' appearance because of security concerns, not pressure from Heineman. Heineman's spokeswoman declined comment Thursday.

At the Colorado event, a crowd estimated by police at 900 listened quietly and occasionally clapped and cheered as Ayers, Churchill and writer-activist Derrick Jensen spoke.

Ayers said he worries less about himself and Churchill than "about the teacher in Denver who can't bring herself to ask the critical question because she saw what happened to Ward Churchill."

He also acknowledged that what the Weather Underground did failed to stop the Vietnam war but he refused to apologize for it.

"I don't claim much for myself, but I'm not going to align myself at this late date with those who want to make war heroes out of criminals and criminals out of heroes," he said.

Churchill said he was battling the university "not for myself but for the possibility of younger generations to hear what they have a right to hear, which is their teachers' version of the truth."

He estimated the university had spent $2.6 million in the process of firing him, not including the costs of next week's trial, and added, "I'm not done with this place yet."

Hilliard, the university spokesman, said he couldn't confirm that figure.

Security concerns briefly threatened Ayers' appearance at the University of Colorado when one of the sponsors balked at a $3,000 university fee for security. An attorney for the students threatened to take court action against the university, but the threat was dropped when the university said it wasn't asking for the money upfront.

Hilliard said Thursday the fee was standard for any event requiring security and that the university still expected to be paid.

During the presidential campaign, John McCain's running mate, Alaska Gov. Sarah Palin, resurrected Ayers' radical past when she accused then-candidate Barack Obama of "palling around with terrorists."

Obama and Ayers served together on the board of a Chicago charity, and Ayers hosted a meet-the-candidate session for Obama at his home in the mid-1990s when Obama first ran for office.