When funding ended for a project to ease trade between the Palestinian territories and Israel, his supporters say, he continued working on it at his own expense. They quote one of his favorite sayings: "Where cargo goes, the economy flows."

In Cuba, Gross was trying to help Cuba's small Jewish community develop an intranet and improve access to the Internet. He was working as a subcontractor to USAID, which supports programs to promote democracy on the island.

He was arrested on his fifth visit. At the time, his family says, he was carrying only cellphones and laptop computers. On another occasion, they say, Cuban authorities had searched his bags and allowed him to enter the country with the equipment he was carrying.

Supporters say Gross was unaware of the risk he was running. During his trial, he called himself "a trusting fool" and said he was "duped" but didn't elaborate.

Cuba analyst Phil Peters, vice president of the Lexington Institute, called the arrest "sad" but not surprising.

"They're still in the Castro administration down there," Peters said. "They tend to tie these programs together with a long series of programs the U.S. government has undertaken to try to change the political order there. Which is exactly what they are."

But he added: "I don't believe the Cuban government has an interest in keeping him in jail for 15 years."

Jaime Suchlicki, the director of the Institute for Cuban and Cuban-American Studies at the University of Miami, says Cuba's intent is clear: to put an end to USAID's Cuba program, and to negotiate an exchange for one or more of the so-called Cuban Five intelligence operatives convicted in federal court of spying on the United States and other charges.

"It was not because he was distributing anything or doing anything so horrible, because there are other people doing it," Suchlicki said. "They decided they may be able to trade him."

U.S. officials reject any equivalence between Gross, who was promoting Internet access, and the Cuban Five, who were accused of infiltrating U.S. military facilities and sending classified information back to the Cuban government.

USAID says it is managing its Cuba program differently, though it declines to specify changes. Nonetheless, officials say, the "fundamental principle" continues.

"The core of the USAID Cuba Program remains in providing humanitarian support, building civil society and democratic space, facilitating the information flow in, out, and within the island," said Mark Lopes, deputy assistant administrator for the agency's Latin America and Caribbean Bureau. "These programs are comparable to what we and other donors do to support democracy and human rights in repressive societies all over the world."

With an exchange not up for negotiation, officials, analysts and supporters say, it is unclear what will win Gross' freedom.

Van Hollen spoke at a demonstration outside the Cuban Interests Section in September.

"I don't know what the point the Cuban government is trying to make, but they should understand the point and message they're sending to the rest of the world," he said. "And that point is that the they fear freedom, and they refuse to do the humanitarian thing."

Gross, who is imprisoned at the Carlos J. Finlay Military Hospital in Havana, has lost 100 pounds since his arrest, according to his wife. She says arthritis now prevents him from exercising.

Cuban authorities have allowed the couple to speak by telephone once a week; she has visited him three times, most recently three weeks ago.

"When people visit him and report back that he looks good, you have to know Alan to understand that he is this jovial, strong-willed person who always puts forth an effort to be in a good mood," she said. "So he's able to pull himself together.

"When I saw him, his mood was a combination of very, very angry and very depressed. He's got a lot of stored-up anger and he has no outlet for it."