FWIW I had a look at various likely databases for John Keane.
Unfortunately I wasn't able to find anyone that fitted the circumstances mentioned (i.e. a New Zealander of that name that passed away overseas from non-natural causes late 1977). However this doesn't necessarily mean he wasn't a New Zealander, nor that there isn't other information to be had.
Peter, your desire to contact his family is commendable; if you should find out he is from New Zealand and/or get any further useful information I'd be happy to do whatever I could to locate them for you - please PM me if anything comes to light.
Incidentally I assume you both have the spelling of his name correct? I've various work colleagues whom I know well, but if asked wouldn't be sure of exactly how to spell their names - this could make quite a difference when searching for detail...