Police have found what appears to be a suicide note at the scene where Mark Minnie's body was discovered.
Minnie was the co-author of the controversial book, The Lost Boys of Bird Island, which details allegations that former apartheid minister Magnus Malan was part of a paedophile network.
Police spokesperson Captain Johan Rheeder confirmed the discovery of the note to News24 on Tuesday afternoon.
Minnie's body was found on the outskirts of Port Elizabeth on Tuesday morning.
Forensic police investigators were combing the scene on the day.
News24 previously reported that the book detailed how three former National Party ministers, including one who is still alive, were allegedly central figures in a paedophile ring that operated during apartheid.
Investigations into Malan – as well as John Wiley, minister of environmental affairs, and another former minister, who was considered a possible successor to then president PW Botha, and who is still alive – were halted by the police, and the investigating officer was hounded from service in the 1980s.
These and other explosive allegations are contained in the book by Minnie, a former police officer, and Chris Steyn, a former investigative journalist.
According to the book, Malan, Wiley and the other minister were involved, along with disgraced Port Elizabeth businessman John Allen, in ferrying coloured minors to Bird Island, in Algoa Bay near Port Elizabeth, where the children were molested and forced to satisfy the older men's sexual fantasies.
Malan died in 2011, while Wiley and Allen's deaths in 1987 were recorded as suicides.