Sindiso Magaqa died on Monday, 53 days after he was shot in an ambush. This week an autopsy was said to have ruled out poison as the cause of death, but added that the causes were "unnatural" and linked to the shooting.
The postmortem appears to support police denials that he was poisoned while in hospital.
Magaqa was shot, along with two fellow ANC councillors, in Umzimkhulu, KwaZulu-Natal, on July 13.
He was secretary-general of the ANC Youth League when Julius Malema, then president of the league, was expelled from the ANC in 2012.Magaqa's family have seen the results of the autopsy and said they wanted a second opinion.
Vuma Magaqa, an uncle, told the Sunday Times that the autopsy had been done on Wednesday and the results had been given to the family.
"The results say there was no foul play, but that he did die from unnatural causes," Vuma said, adding that the report linked his nephew's death to the shooting.
He said the family were not entirely satisfied.
He would not comment on the poisoning rumours and said there would be further tests and that the family wanted another opinion on the cause of death. No arrests have been made in connection with the shooting, but police said they were closing in on the killers.
A senior police officer said Magaqa had been murdered because he had exposed corruption related to a tender for the upgrading of a hall in Umzimkhulu.
The budgeted cost of the hall's renovation had been about R4-million, but it had ballooned to R37-million.
"The case is now very sensitive in relation to a possible arrest," the officer said.
Malema, who remained a close friend of Magaqa, said the family still had questions about Magaqa's sudden downturn in health."His wife [Gugu Magaqa] cannot come to terms with the fact that she spent a lot of time with him in hospital and she saw him recovering," said Malema.
"The next thing he was complaining about his stomach. After three days he gave in. I wouldn't say the family are suspicious, but they need answers. They are relying on the medical reports."
Magaqa is the fifth councillor to be murdered in Umzimkhulu since April. The two councillors wounded along with Magaqa, Jabu Msiya and Nontsikelelo Mafa, are still in hospital.
Police crime intelligence officers have been assigned to the case.
Thabiso Zulu, a friend of Magaqa and a fellow ANC member, said the hall tender had been the reason for the murder.
"Around September/October last year Comrade Sindiso handed over to me documents in the presence of a [provincial executive] member that were meant to prove an alleged corruption ... which amounts to R37-million. I did what I was supposed to."
Documents were handed to the Hawks and National Treasury.
There have also been claims that the killing was linked to a leadership contest in the Harry Gwala region.
Magaqa was a candidate for at least two ANC positions in the area.MURDERED THIS YEAR
• March 6: Sibusiso Sithole, Richmond municipal manager
• April 3: Thandazile Phoswa, Richmond deputy mayor
• April 23: Khaya Thobela, Umzimkhulu municipality speaker and ANC deputy secretary in the Harry Gwala region
• May 11: Khaya Gcwaba, former Umzimkhulu councillor
• May 23: Mduduzi Shibase, Umzimkhulu councillor
• June 8: Florence Nene, Umzimkhulu councillor killed in a mysterious car crash
• June 29: Sifiso Mkhize, Richmond councillor, attacked; dies the next day
• July 13: Sindiso Magaqa, a former ANC Youth League secretary-general and Umzimkhulu councillor, is shot, as are councillors Nonsikelelo Mafa and Jabu Mzizi. Magaqa dies in a Durban hospital on September 4
• August 8: Ntokozo “Lithi”Maphumulo, former Umdoni councillor
• August 30: Kwazi Everlast Mkhize, Umkhambathini councillor..