Hi Gary, my partner Jess McDonald is granddaughter to Murdoch and it rings bells that Murdoch is buried at St James Angelican Church on Church Street, Mangere Bridge but she has attempted to try find his headstone but no luck as you say Roberts grave is unmarked Murdoch's maybe as well. She was told that her grandfather Murdoch maybe buried on the left-hand side of the cemetery close to a tree. Whakatane is where Murdoch was raised and adopted in by the Cassin Family, after Mary tira Witika he later married Constance who is my partners grandmother. Murdoch and Constance had 6 children which one of whom is my partners father Donald McDonald, her father was also abandoned as a child at the age of 9 and was raised up in Auckland. My partner and her father have no info on the whereabouts of his siblings other than his mother passed away when my partner was 10 years old. If this is of any help to your research, please don't hesitate to contact my partner Jess on 02108203073