Saajid Badat, 34, who eventually backed out of the plot with Reid, testified Monday via video hookup from Britain that he trained under bin Laden -- Abu Ghaith's father-in-law -- in Afghanistan before the Sept. 11, 2001, terrorist attacks on the United States, the New York Daily News reported.
Abu Ghaith, 48, is the highest-ranked al-Qaida figure to be tried on U.S. soil since the attacks.
Badat admitted he received instructions from al-Qaida leaders in late 2001 to detonate explosives hidden in his shoes.
"It was supposed to be a domestic United States flight," Badat said.
Abu Ghaith is charged with supporting terrorists and conspiring to kill Americans as an al-Qaida spokesman. Federal prosecutors charge he knew al-Qaida was planning future jetliner attacks.
Badat said he didn't remember meeting Abu Ghaith in Afghanistan and that he doesn't know whether the Abu Ghaith knew of the shoe bomb plot.
Badat was sentenced to 13 years in prison in Britain for conspiring to damage an aircraft, but was released after six years when he agreed to cooperate with prosecutors, the Daily News said.
Reid pleaded guilty to terrorism charges in the United States in 2002 and was sentenced to life in prison.