Hors la loi : Rester en prison

Suspected of attempted murder, escape, burglary, or sexual assault, six individuals were detained following their arrest, either caught in the act or after an investigation. They enter prison to serve an initial "provisional" sentence while awaiting trial, a temporary measure that can sometimes drag on due to lengthy judicial procedures. What does detention mean when it becomes indefinitely provisional, or when its duration is challenged in appellate courts? What, then, is its legitimacy?