Looking for name and author of book: I read it in the '80's I think! About a couple sailing to south seas, were hijacked and killed. True story about California couple (I think). Murders were eventually arrested and convicted of piracy and murder. I remember it being about 500 pages with some photos.

Possibly "The Sea Will Tell" by Vincent Bugliosi.

I agree, it sounds like "The Sea Will Tell". It was also a made for TV movie sometime around 1990.