"I am not backing off an inch," said Ward Churchill on Tuesday, drawing an ovation from a standing-room-only crowd of about 1200 students and backers gathered in a ballroom.
"I owe no one an apology."
Churchill, who filed a lawsuit earlier in the day after officials at the state-funded university had threatened to cancel his speech, said his central message was that the 11 September 2001 attacks had been provoked by US foreign policy.
"Naturally and inevitably, what you put out will blow back on you and that's what happened," Churchill said.
In his essay, Some People Push Back, written shortly after 9/11, Churchill said the hijackers had mounted "counter attacks" in the face of hostile US policy in the Middle East and a campaign of "genocide" against Iraq through the trade sanctions imposed after the first Gulf war.
Victims not innocent
In the essay, later revised for a book, Churchill also said that World Trade Centre victims could not be seen as innocent, calling them "little Eichmanns", a reference to German second world war criminal Adolf Eichmann.
"True enough, they were civilians of a sort," he wrote.
"Naturally and inevitably, what you put out will blow back on you and that's what happened"
Professor Ward Churchill, University of Colorado
"But innocent? Gimme a break. They formed a technocratic corps at the very heart of America's global financial empire."
Churchill, a veteran Native American activist, first attracted widespread notice last month after Hamilton College in New York cancelled a scheduled appearance, citing threats against him and others who had been scheduled to appear.
The University of Colorado launched an investigation, a first step towards possibly firing the professor.
Scholars have rallied to the defence of what they see as the free-speech rights at stake in the case, saying the firing of a tenured professor over unpopular remarks would threaten academic freedoms.
Churchill has resigned as chairman of the university's ethnic studies department but has threatened to sue the school if he is fired.
Churchill felt sorry for some 9/11
victims as well as Iraqi children
He said he felt sorrow for "the firefighters, food service workers, broom pushers and passersby" who died in the 9/11 attacks.
But he added that he also felt sorrow for the 500,000 Iraqi children he said had died as a result of the sanctions imposed on the country after the first Gulf war.
He also said his initial published remarks had been deliberately miscast by conservative pundits.
"Nowhere in there did I justify the killing of innocent people," he said. "Those words are not there."