Lawyers and supporters of the chief suspect in a deadly attack on a Paris synagogue in 1980 expressed disappointment at his being denied release for an eighth time on Tuesday.
Hassan Diab, 63, had been ordered released pending the conclusion of the investigation into the case, but the decision was overturned on appeal.
The Lebanese-Canadian sociology professor is accused of being part of a Palestinian group blamed for the bombing on October 3, 1980 that left four dead and around 40 injured.
Diab has been detained in France since being extradited from Canada in 2014.
While the 37-year-old case has been investigated by French authorities, he has maintained his innocence and denied being a member of the Popular Front for the Liberation of Palestine (PFLP).
Roger Clark, a former director of Amnesty International and member of a Diab support group, told AFP that his continued detention is "extremely disappointing."
"The decision to deny his release reflects the ridiculous nature of what's going on in his case. It's grotesquely absurd," he said.
Clark met with Diab in prison during a recent trip to Paris.
"He expressed a lot of disappointment. Physically he's finding it quite difficult, his health is okay but not great, his mental state is a challenge for him, and he's having difficulty remaining optimistic," Clark said.
The bombing at the synagogue on Rue Copernic in Paris was the first major attack on a Jewish site in France since World War II.
The prosecution has pointed to a sketch of the bomber resembling Diab, the discovery of a passport in his name with entry and exit stamps from Spain, where the bomber is believed to have fled, and testimonies that Diab was a member of the PFLP in the early 1980s.
Diab insists that he was in Beirut at the time of the attack, taking university exams, which witnesses have corroborated.
The facts raise "doubts" about Diab's presence in France and other evidence implicating him in the attack, said the judge who had ordered Diab's release, according to a source close to the case.
"We are confronted with an unprecedented and ubiquitous situation," his lawyers told AFP.
"As almost always in the most serious cases, the liberation and recognition of the innocence of the one who was wrongly accused takes time, but it will come."
© 2017 AFP