A washing machine repairman who was publicly named as a person of interest in the high-profile case of missing boy William Tyrrell has begun legal proceedings against the state of New South Wales, claiming malicious prosecution by NSW Police and malfeasance in public office.

William "Bill" Spedding had been at the home of William's foster grandmother in the week prior to the little boy's baffling disappearance.

Bill Spedding on the ABC program Four Corners. Credit:Four Corners/ABC

Strike Force Rosann investigators spoke to Mr Spedding in a marathon six-hour interview at Port Macquarie police station in 2014 and raided the Bonny Hills home he shared with his wife Margaret after neighbour Dean Pollard told detectives he "definitely" saw Bill's van driving up a bush track the day William vanished.

Mr Pollard has since said before the Coroner's Court that he definitely saw a van that looked similar to Mr Spedding's, not that he definitely saw that exact van.