The son of South Australian wife killer Peter Dansie has opened up about the drowning murder of his wheelchair-bound mother.

He spoke to 9News exclusively about the murder, where Grant’s mother Helen drowned after her husband Peter pushed her wheelchair into a pond in the Adelaide parklands in April 2017.

"To think that's how she spent her last moments, just in utter fear in a dark cold, pond and there was nobody to help her… there was nothing she could do, she was completely alone," Grant said sadly.

In December, Peter was sentenced to 25 years behind bars for Helen’s murder and Grant revealed how he helped detectives arrest his father.

"I always knew that he was a horrible person, a vindictive person, focused on power and control, but I didn't think he had it in him to do that," Grant said of his father.

Peter Dansie

Grant said that detectives had just two questions for him.

"They had two questions – first, are you willing to testify? And second, are you willing to wear a wire?"

Grant quickly agreed to both and met with his estranged father for the first time in 17 years to hear why he did it.

"He didn't care. He showed no emotion. He showed no remorse. He showed no love for this woman," he said.

Inconsistencies in Peter’s story to his son helped police arrest and ultimately convict the 70 year old.

However, Grant worries as to how he’ll tell his children what happened to their grandparents.

"I still haven't concluded how to do that properly - it's kind of hard. We've just said that their grandparents have died," he said.

As Peter is trying to appeal his conviction, his son is confident he won’t be going anywhere.

"The thought that he will be in jail for life is actually quite nice," Grant said.

Photo credits: 9News