An 86-year old man who faced four trials over the death of a Scottish woman more than two decades ago has been sentenced to more than six years in jail.

Ronald Leslie Pennington was found guilty in July of killing Cariad Anderson-Slater in 1992. She was last seen going into the Perth home Pennington lived in at the time. Her fate was unknown until her remains were uncovered in 2011 by workers digging up the house's backyard. A cause of death has never been determined.

Pennington was found guilty in 2012 of manslaughter, but successfully appealed and a new trial was ordered. The second and third trials failed to reach verdicts.

On Wednesday, Supreme Court of Western Australia Justice Michael Corboy sentenced him to six-and-a-half years in jail.