The prisoner has been languishing in the jail for the last many years.

convicted : having been declared guilty of a criminal offence by the verdict of a jury or the decision of a judge.
suffering : the state of undergoing pain, distress, or hardship.
attempting : make an effort to achieve or complete (something difficult).
avoiding : keep away from or stop oneself from doing (something).
languishing : be forced to remain in an unpleasant place or situation.


Synonym of languishing is suffering