A man accused of killing three people over 13 years allegedly had a “thing” for knives and told two people he had stabbed an “old lady”, a court has heard.

Steven Leslie Hainsworth is standing trial in South Australia’s Supreme Court charged with the alleged murder of his neighbour Phyllis Harrison, 71, his aunt Beverley Hanley, 64, and Stephen Newton, 55, between 1998 and 2011.

Mr Hainsworth’s former prison mate, Kryss Pumpa, gave evidence in court on Tuesday that the alleged serial killer confessed to stabbing Ms Harrison before throwing the knife he used in nearby bushes.

Prosecutor Martin Hinton KC asked Mr Pumpa whether he had ever discussed Ms Harrison with Mr Hainsworth in the short time they were both inmates at Mount Gambier Prison around 2011.

“[He] basically [said] that he had stabbed her and had thrown the knife in the bushes,” Mr Pumpa said.

Steven Leslie Hainsworth is accused of murdering three people.

Mr Pumpa said Mr Hainsworth also told him he had been getting “a lot of pressure from the police” and he had “bashed a relative”.

The prosecutor asked Mr Pumpa if Mr Hainsworth had ever spoken to him about another alleged murder.

“Yeah, a relative he bashed with a blunt object,” Mr Pumpa said.

Mr Pumpa told the court Mr Hainsworth did not disclose who the relative was, or where or when it happened.

In cross-examination, Mr Hainsworth’s defence lawyer, Andrew Fowler-Walker, asked Mr Pumpa if he considered himself a “fraudster” after being convicted of fraud.

“Yeah, pretty much, but I’m not a granny killer,” Mr Pumpa said.

Phyllis Harrison, Beverley Hanley and Stephen Newton were allegedly murdered. (SA Police)

Lorrilea Crilly told the court Mr Hainsworth, her then-friend and lover, had said to her “a couple of times” that he “bashed and stabbed an old lady” at Elizabeth.

“I didn’t take much notice,” she said.

Ms Crilly said Mr Hainsworth once told her about it in front of a “few” other people.

“It was just in conversation with people around,” she said.

Ms Crilly told the court she did not take Mr Hainsworth’s claims seriously, saying “he was a big talker, he talked a lot of shit”.

Ms Crilly said Mr Hainsworth often carried a knife with him because he “had a thing” for them.

“I can’t recall what sort of knife but he had a thing for them back then,” she said.

The court this week released an interview between police and Mr Hainsworth in the weeks following the death of Ms Harrison.

Mr Hainsworth told police he had heard from the news that Ms Harrison was allegedly murdered.

On Monday, forensic pathologist Ross James told the court Ms Harrison was stabbed 16 times in her chest and neck, severing major arteries.

“I think the death was quite obviously, in this case, due to haemorrhage due to multiple stab wounds to the chest and necks,” Dr James said.

The court heard Ms Harrison had bruising on the back of her head and cuts on her left hand.

The trial continues.