A repeat drink-driver responsible for killing three people in separate incidents on WA roads walked free from prison on Monday - and the son of one of his victims has voiced his concerns that he will "do it again".

Kevin David Barron was four times the legal blood-alcohol limit when he ran over and killed John Donnelly, as the father-of-three walked along the side of a Sawyers Valley road in 2007.

On Monday, he was released from prison after serving seven-and-a-half years for the 60-year-old's death.

Mr Donnelly was the third innocent victim to die as a result of Barron being behind the wheel, after he previously killed his brother and a friend in separate driving incidents.