Saajid Badat was sentenced in 2005 to 13 years in jail as a co-conspirator in the notorious shoe bombing plot in December 2001, a time of worldwide concern over air travel after the September 11 attacks in the United States.
The 34-year-old has been dubbed a "supergrass," slang for informant, by the British media for agreeing to testify against a slew of former associates.
He was released early from prison in Britain, where authorities have given him accommodation and financial help, and he gave evidence from an undisclosed location yesterday because he faces arrest in America.
The prosecution showed the jury two videos of the defendant in October 2001 threatening Americans with a "storm of airplanes," which they say implicates him in the shoe bomb plot.
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"The storm shall not lessen especially the storm of the airplanes," Abu Ghaith shouted in one of the propaganda clips.
But the defense says there is no evidence tying Abu Ghaith, 48, to the conspiracy and brands Badat, who looked worried and unhappy throughout more than two hours of testimony, the real terrorist.
Fluent in English, Arabic, Urdu and Gujarati, Badat said he smuggled explosives from Afghanistan to Britain in late 2001 after being recruited by al-Qaeda to blow up jetliners with bombs hidden in shoes.
Fellow British recruit Richard Reid, known as the shoe bomber, is serving a life sentence in the United States for trying to blow up a Paris to Miami flight in December
Badat, then 21, said he worked directly with Reid from October to December that year in Afghanistan, and testified that they were supposed to blow up different planes.
The witness, who grew up in a pious Muslim family in the English town of Gloucester, said he was introduced to the idea of violent jihad in London in 1997.
In 1998 he went to Bosnia, where he met veterans of the Balkans war and was taught how to use weapons. In 1999, as a 19-year-old he traveled to Afghanistan, via Dubai and Pakistan, to train for jihad.