New terrorism charges await a German man who provided critical support to Osama bin Laden before the Sept. 11 attacks and will face trial in the U.S. after serving most of a terrorism-related prison sentence in France, authorities said Wednesday.

Christian Ganczarski, 51, was charged in a newly unsealed indictment in Manhattan federal court with conspiring to kill Americans and supporting terrorists.

Top U.S. law enforcement officials portray Ganczarski as a key al-Qaida supporter in the two years before the Sept. 11 attacks, saying he provided technological guidance and software, knew at least one of the 9/11 hijackers and sat in the front row of a bin Laden speech in January 2000 with the son of one of al-Qaida's top operatives on his lap.

In a release, Manhattan U.S. Attorney Geoffrey S. Berman said Ganczarski "provided critical support to the most prolific terrorists of our time."

He added that Ganczarski participated in the planning of plots to kill Americans with high-level al Qaeda terrorists, including bin Laden and Khalid Sheik Mohammed, the self-described architect of the 9/11 attacks.

The U.S. seeks Ganczarski's extradition from France, where he has been imprisoned for the last 15 years after he was convicted and sentenced to 18 years in prison for his role in a 2002 attack on a synagogue in Tunisia that killed 21 people.

Last week, he was charged with stabbing three prison guards, leading to his transfer to another prison in northern France and sparking protests by French prison guards outside scores of jails across France.

William F. Sweeney Jr., head of New York's FBI office, said Ganczarski arranged meetings between senior officials in al-Qaida and other like-minded individuals who wanted to attack U.S. interests.

"While he's spent the past fifteen years behind bars in France, we haven't forgotten his allegiance to those who have threatened our interests both at home and abroad," he said.

New York Police Commissioner James P. O'Neill said Ganczarski lived in al-Qaida's camps and guest houses while he worked with bin Laden and men who planned and executed plots to bomb U.S. embassies in Africa, killing 225 people.

After the Sept. 11 attacks, Ganczarski helped al-Qaida maintain weapons systems that would be used to attack U.S. soldiers and their aircraft, O'Neill said.

Authorities said Ganczarski was in Germany at the time of the Sept. 11 attacks and indicated afterward that he had been aware that a significant event was about to occur.