Syrian security services released Palestinian refugee Fouad Kassem after five years in detention.
Kassem was arrested in January 2014 after his house in the Hama refugee camp was raided.
The Action Group for Palestinians of Syria (AGPS) said the Syrian security services continue to hide the fate of more than 1,756 detainees in their prisons, despite demands for their release.
According to the group, the detainees include children, women, elderly persons, and entire families, hundreds of whom have died as a result of torture.
In August 2012 Syrian regime forces dropped two missiles on the largest Palestinian refugee camp – Yarmouk – killing more than 20 Palestinians and wounding hundreds more.