A US prison official said Wednesday that Mahmoud Abouhalima, an Egyptian serving a life term in the United States for conspiracy as the organizer of the 1993 World Trade Center bombings, remained in prison in Colorado, contradicting reports that he had been returned to the Egyptian capital. Egyptian security officials said Abouhalima was returned to Cairo airport by US guards Wednesday night and handed over to Egyptian authorities. The security officials spoke on condition of anonymity because of the sensitivity of their positions. It was not known why Abouhalima, who is about 45, would have been returned to Egypt. Krista Rear, a spokeswoman for the maximum-security federal prison in Florence, Colorado, said Wednesday that Abouhalima remains an inmate at that facility. Lawrence M. Stern, Abouhalima's most recent attorney, said from the United States he had heard nothing about Abouhalima's release and would be shocked if Abouhalima had returned to Egypt. Six people died and more than 1,000 were injured in the bombing of the towers that were later destroyed when two jetliners crashed into them on Sept. 11, 2001, killing nearly 3,000 people.