HELEN McMahon loved the solitude of the expanse of beaches stretching along the Mornington Peninsula.

She would have had every right to think there was nothing to fear here, apart from the treacherous surf and rips on this exposed coastline.

The 47-year-old would have had no reason to think this peaceful area, where she sunbathed, would be the hunting ground of a killer.

On February 13, 1985, Ms McMahon headed for the Rye area to take in the summer sun.

media_camera Helen McMahon was murdered at Rye in 1985.

Later that day, her battered body, naked but with a towel placed over it, was found.

Had she known what we now know about Peter Dupas, she might have had second thoughts about the beach visit.

Dupas was serving a jail sentence for rape but was out on prerelease day leave the day of the McMahon murder.

He went back inside to finish his stretch but, by early March, was behind bars again.

This time, Dupas had followed, then raped, a young woman at knifepoint at Blairgowrie, also on the Peninsula.

Dupas has long been a suspect in the murder of Ms McMahon, but has never been charged. He was questioned but denied having anything to do with the crime.

Since then, he has been convicted over the murders of Margaret Maher, found dead and mutilated at Somerton in 1997; Mersina Halvagis, who was stabbed to death at Fawkner Cemetery in the same year, and psychotherapist Nicole Patterson, fatally stabbed in her Northcote home in 1999.

Thirty years after Helen McMahon’s murder, police have posted a $1 million reward for anyone able to help them arrest and convict whoever was responsible.

Anyone able to help can call Crime Stoppers on 1800 333 000 or visit the website www.crimestoppers.com.au

mark.buttler@news.com.au