“The challenges that come with the passage of time and trying to work so far from home have simply become too difficult for me and my extended family,” he said.
The case has been mired in pretrial hearings over what evidence would be admissible at the national security trial, which is expected to last more than a year when it eventually starts.
The defendants were held from 2003 to 2006 in the C.I.A.’s secret overseas prison network, known as black sites, complicating efforts to move past the pretrial litigation phase. A key issue is whether the accused voluntarily confessed at Guantánamo after years in which they were deprived of sleep, kept in solitary confinement and interrogated with violence, including waterboarding.
For more than a decade, Mr. Ryan, 62, had close interactions with the Sept. 11 families, both at Guantánamo hearings and in private meetings prosecutors periodically held in Massachusetts, New York and Florida.
“All that knowledge, I’m sad to see him go,” said Kathleen Vigiano, whose husband, Joseph Vigiano, a New York police detective, and brother-in-law, John Vigiano Jr., a New York firefighter, were both killed at the World Trade Center.