Professor Dr Hasan Zafar Arif, MQM-London's deputy convener, was found dead in a car in Karachi's Ilyas Goth area on Sunday, police said.
"The body of Hassan Zafar Arif, son of Maqbool Hassan, 70-72-years-old, was found from car number ANC-016, Lancer silver at Ilyas Goth," station house officer at Ibrahim Hyderi police station confirmed.
"The body was shifted to Jinnah Postgraduate Medical Centre (JPMC)," he added.
The SHO said that the cause of death will be ascertained after an autopsy is carried out. "Further investigations are ongoing," he said.
At JPMC, Dr Seemi Jamali said that no signs of torture or bullet wounds were found on the body.
She added that further details will come forward once the autopsy is complete. The body has been shifted to the mortuary to ascertain exact cause of death
Senior Superintendent Police Malir Rao Anwar also said that no marks of torture were found on Dr Arif's body.
Dr Arif was a former associate professor at the Philosophy Department in University of Karachi.
Editorial: Dr Arif’s persecution
According to MQM legal adviser Advocate Abdul Majeed, Dr Arif was with him on Saturday evening but left earlier than usual as his daughter was leaving for London. Majeed said he received a call from Arif's wife in the morning, saying he had not returned home. He was a resident of DHA Phase-VI.
He demanded that a proper inquiry be carried out into the death as the location where the car was found was not on Dr Arif's route. "On Saturday evening, he drove the car himself from his office at Fareed Chambers to his residence in DHA. But his body was found in the rear seat of the car," he added.
PPP Chairman Bilawal Bhutto Zardari expressed deep sorrow and concern over the media reports about Dr Arif's "disappearance and unnatural death." He also asked the provincial home minister to inquire into the reports.
"Professor Hassan Zafar Arif was a progressive political activist and he had played an active role during the struggle against dictatorial rule of General Zia," Bhutto said in a statement.
In October 2016, Dr Arif was taken into Ranger's custody from outside the Karachi Press Club, where he was due to address a press conference along with other leaders of MQM-London.
He had been booked for allegedly facilitating and listening to a controversial speech of MQM founder Altaf Hussain in which he reportedly tried to outrage religious feelings, criticised the military establishment and asked his workers to extort money from the traders.
In April 2017, he was released from Central Jail Karachi after an Anti-Terrorism Court (ATC) issued his release order.
Dr Arif was an associate professor at the University of Karachi and a former fellow at Harvard University.