Humpel, 63, became a household name in Port Elizabeth in the mid-1990s after cracking the Alison Botha rape and attempted murder case, among several other high-profile investigations.
Since news of his death on Sunday, messages of support and condolences have flooded in on social media.
Friends and family called Humpel an outstanding detective, an avid dog lover and a man who gave back to the community.
Humpel’s most high-profile case was in December 1994, when Botha was hijacked and taken to a remote spot at Noordhoek, where she was raped and stabbed more than 30 times, and her throat slit.