Christian Ganczarski, aka Abu Mohamed -- a German citizen born in Poland -- is at present lodged in a prison in France, where he spent last 15 years.
In March 2000, he attended a meeting in Karachi at which US and Israeli targets for terrorist attacks were discussed.
A sealed indictment in this regard was made public yesterday.
Manhattan US Attorney Geoffrey S Berman said: "Christian Ganczarski, a German national, allegedly provided critical support to the most prolific terrorists of our time".
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Ganczarski allegedly provided Al-Qaeda with expertise in logistics, computers, radio communications and the maintenance of weapons systems that would be used against Americans soldiers after the 9/11 attacks, said New York Police Commissioner James P O'Neill.
"He rubbed shoulders with Osama Bin Laden and the men who planned and executed plots from the bombing of US embassies in East Africa that killed 225 people, to the 9-11 attacks that cost 3000 lives, most of them here in New York City," he said.
He traveled from Germany to Pakistan and Afghanistan on at least five separate occasions between 1999 and 2001.
During these trips, he became associated with Al-Qaeda and developed personal relationships with bin Laden, Abu Hafs el Masri, al Adel and Mohammad.
Ganczarski lived at times with his family at al Qaedas fortified compound near Kandahar. At other times, he lived in guest houses and other facilities operated by Al-Qaeda in Afghanistan, said ONeill.
He participated in Al-Qaedas efforts to kill Americans in a number of ways, such as providing al Adel and other Al- Qaeda members with technological guidance and hardware, including computers, radios and other communications equipment.