Dr Riaz Ahmed, assistant professor in the Applied Chemistry department at Karachi University in Pakistan and elected representative on the university council, was picked up by security forces on Saturday.
He was seized outside Karachi Press Club together with Professor Meher Afroz Murad, who has now been released.
He was about to address a scheduled press conference calling for the release from prison of a former colleague, the retired Karachi University professor Dr Zafar Hassan Arif, who has been detained since October 2016.
Media reports reveal that he was arrested by the paramilitary Sindh Rangers.
He has now been charged with the possession of an unlicensed 9mm pistol, and sent to Karachi Central Prison. His lawyer was to make an application for bail today, Monday.
A human rights defender and renowned Marxist intellectual, Dr Riaz has been a strong, non-violent voice calling for freedom of expression. For example, he called for the release of missing persons such as the Baloch intellectual, Wahid Baloch, held for five months, July-December 2016.
The call has gone out to trade unions, elected officials, international human rights organisations and other concerned organisations and people to take notice of the illegal detention of Dr Riaz Ahmed and help ensure his immediate release.