U.S. officials tell CBS News Correspondent Jim Stewart that Padilla had contacted a Florida man from overseas before leaving on his mission and was apparently en route to meet him when he was arrested.
Federal investigators monitored the communication between Padilla and Palestinian Adham Hassoun of Sunrise, Fla. They arrested Hassoun earlier this month following months of surveillance.
Hassoun is now being held on an immigration charge at an INS facility and is considered a flight risk. U.S. officials describe him as an "important link" not only to the Padilla investigation, but possibly to a suspected U.S.-based al Qaeda network awaiting orders for future attacks.
Sources said domestic intelligence intercepts have now convinced officials that such a network of al Qaeda fundraisers and operatives exists in the United States.
A number of people are under surveillance. None is believed to have had a supporting role in the 9/11 attacks. Some may have been slated to assist Zacarias Moussaoui - the so-called "20th Hijacker" - who senior officials now believe, in fact, was not scheduled to be part of the Sept. 11 attacks after all, but was to have carried out a separate, unknown mission.
Officials also said there is no known connection between Hassoun, a 13-year U.S. resident who lives with his family, and the 9/11 hijackers. Hassoun attended the same mosque as Padilla, a former gang member who converted to Islam while living in South Florida. Hassoun is also well known in the Muslim neighborhoods of South Florida for his financial and vocal support of extremist Islamic groups, although friends said today such actions were a political statement only.
"I would consider him that he's against violence, but he has a strong tongue, you know, he has a strong tongue!" said Sofian Abdelaziz, with the American Muslim Association of North America.
The FBI did not want to pick Hassoun up, preferring instead to continue their surveillance and see where it would lead them. Sources said the bureau's hand was forced when agents monitored a phone call from a Miami newspaper reporter to Hassoun seeking information about the Padilla case and feared that their subject might flee.
Padilla, 31, remains in military custody. He was arrested May 8 in Chicago when he got off a plane from Pakistan. He was born in Chicago and lived in South Florida in the 1990s, when he converted to Islam and began calling himself Abdullah al Muhajir.
He was arrested by Sunrise police in 1991 on a handgun-related charges. While in the Broward County Jail, he was accused of battery on a jail officer and resisting without violence in January 1992. Padilla was last in the United States in 1998. After that he traveled mostly in the Middle East, officials said.
Moussaoui is currently making waves in a Virginia courtroom, where, most recently, he has been granted the right to represent himself in court. He is charged with six counts of conspiring with Osama bin Laden and his al Qaeda network to carry out the hijacked plane attacks, in which 19 hijackers died. U.S. officials have said Moussaoui may have been preparing to be the 20th hijacker. Several of the counts carry a possible death sentence.
Moussaoui, a 33-year-old French citizen, had been in custody on immigration charges when the Sept. 11 attacks occurred.