Haroun Fazil, from the Comoros Islands in the Indian Ocean, is alleged to have been the explosives expert. He is still at large, despite an intensive hunt led by US law enforcement authorities. There is a $2m (pounds 1.2m) reward for his arrest.
He is alleged to have rented a villa near Nairobi where the bomb was built, to have driven a truck which accompanied another vehicle that contained the bomb, and to be a key figure in Mr bin Laden's Al-Quaida organisation.
The arrest of another man gives further insights into America's long campaign against Osama bin Laden, a wealthy, former Saudi Arabian that Washington believes was the masterminded behind the attacks on the embassies in Kenya and Tanzania.
The man who was arrested, Wadih El Hage, was living in Dallas, Texas. He is allegedly a former secretary to Mr bin Laden, and is charged with lying to the authorities about his past connections to him.
He also said he did not know any of the suspects in the Nairobi blast, though one of them said that he knew Mr Hage well. He was not charged with participating in the bombing. His American wife, April Ray, said she was distraught about his arrest. "I'm having a hard time dealing with it," she said.
There are two other bombing suspects in custody, Mohamed Sadeek Odeh and Mohamed Rashed Daoud al-Owhali. They have each been charged with 12 counts of murder. Mr Hage had been questioned by US authorities last September, months before the bombings. America is believed to have access to several former members of Mr bin Laden's inner circle, who are providing information.Reuse content