A notorious child murderer suspected of killing at least four more people has taken his remaining secrets to the grave.

Bevan Spencer von Einem died in prison while serving a life sentence for the 1983 murder of teenager Richard Kelvin, the son of former Nine News presenter Rob Kelvin.

The 79-year-old has long been suspected of having killed four more young men, but South Australian Premier Peter Malinauskas said his refusal to co-operate with police meant his legacy of devastation could never be undone.

“He chose silence —callous, deliberate silence—denying victims’ families even the faintest chance of closure,” Malinauskas said in a statement on Saturday.

“His decision to take critical information to the grave is an act of cruelty in its own right.

“His death marks the end of a life defined by calculated brutality.”

Von Einem’s crimes are considered some of the most horrific ever committed in the southern state.

After abducting the 15-year-old teenager from a bus stop, he kept him captive for weeks, drugging, torturing and sexually assaulting him before dumping his body in the Adelaide Hills.

Richard was one of five youths or young men brutally murdered in and around Adelaide during the late 1970s and early 1980s.

At the time, it was widely suggested the killings were the work of a group known as The Family, which was thought to involve people with high societal standing.

Von Einem remains the only person to have been convicted over any of the deaths.

He was charged with two more murders, but both charges were dropped because of a lack of admissible evidence.

Von Einem was also ordered to serve an extra three-month jail term in 2009 for possessing child abuse material while in prison.

“Today, my thoughts are with the families of his victims,” Malinauskas said.

“The greatest tragedy is that they may never know the full truth because of his deliberate and selfish silence.

“Their strength in the face of unimaginable suffering deserves our deepest respect and support.”