The MQM had claimed that senior party leader Farooq Sattar's coordinator Aftab Ahmed died while he was in Rangers' custody in Karachi.
42-year-old Ahmed, a father of five, was arrested from Karachi.
A high-level inquiry ordered by army chief General Raheel Sharif has found that a senior worker of the MQM who died in the custody of the paramilitary Rangers was subjected to torture.
Over 35 per cent of the body was covered in bruises and abrasions, the postmortem report said yesterday.
The rangers, however, had claimed that Ahmed had died from a heart attack.
The MQM held peaceful protests here demanding an independent inquiry into the death of Ahmed. The MQM had been complaining that it is being targeted as part of the military operation launched in 2013.
Senior party leader Sattar said that the autopsy proves that their party colleague was tortured prior to his death.
"Around 3,000 of our workers bear torture marks on their bodies. It is the responsibility of the law enforcement agencies to expose such black sheep amongst them and get rid of them," he said.
