Mohammad Khan, the father of Naqeebullah Mehsud — a Waziristan native killed in a staged encounter in Karachi in January 2018 — passed away on Monday.
Khan had been pursuing Naqeebullah's murder case since his demise.
In a tweet, activist and lawyer Jibran Nasir said Khan had passed away after battling cancer, adding that his funeral prayers would be offered in Khyber Pakhtunkhwa's Tank district on Tuesday at 10am and in his village Makeen at 2pm.
"He was a remarkable man with great resolve, we must carry forward his struggle for justice," said Nasir.
In a condolence message issued by the Inter-Services Public Relations (ISPR), Army Chief Gen Qamar Javed Bajwa expressed "heartfelt grief" over Khan's demise and prayed for the soul of the deceased.
"Efforts to ensure the provision of justice as promised to him shall be pursued," the army chief was quoted as saying by the ISPR.
Khan's son, Naqeebullah, who hailed from South Waziristan, was among the four suspects killed in an 'encounter' with a police team headed by notorious encounter specialist former SSP Rao Anwar and his team in the Usman Khaskheli Goth on the outskirts of Karachi last year.
Dawn Investigations: Rao Anwar and the killing fields of Karachi
Anwar had stuck to the claim that the deceased was a Tehreek-i-Taliban Pakistan (TTP) militant but a spokesperson of the outlawed TTP's South Waziristan chapter had termed Anwar's claim as "baseless", clarifying that Naqeebullah had no links with the banned militant outfit.
Naqeebullah's family also disputed the former SSP's claim, saying that the 27-year-old had no links with any militant organisation.
Naqeebullah — whose name is given as Naseemullah on his national identity card — was a shop owner fond of modelling, a relative of the deceased had told Dawn.
In January, an anti-terrorism court in Karachi had declared Naqeebullah and three others innocent and quashed the cases filed against the four accused who had been killed in the staged police encounter.
In March, an ATC indicted Anwar and 17 others for the murder of Naqeebullah in the fake encounter.
Anwar as well as former deputy superintendent of police Qamar are currently out on bail. Eight other policemen involved in the incident are in jail while former SHOs Amanullah Marwat and Shoaib Shaikh are absconders in the case.