On the seventh day of Malcolm Rewa's third trial he took the stand as a witness to testify in his own defence over the killing of Susan Burdett.

He claims he was in a secret sexual relationship with her but the prosecutor says Rewa is lying in an effort explain how his DNA was found at the crime scene.

The 65-year-old serial rapist was convicted of Burdett's rape in 1998 - but two juries that year were unable to decide whether he was also responsible for her death.

Today, he walked past the press bench from the dock with the help of his cane. He was wearing a white, collarless long-sleeve shirt and sporting a new haircut.

He then swore on the Bible to tell the truth.

While serving a preventive detention sentence for his several rape convictions, Rewa explained he had found Christ after "such a harsh, possibly nasty life".

"I walked the Christian walk," he said of his past 23 years in prison.

"It taught me a different way of life - to be accepting. I accepted people for who they were. I learnt to understand, I learnt empathy.

"In prison you get all walks of life - some of the crimes are worse than others - but unless it's against you, you accept them for who they are, not what they've done."

When his lawyer Paul Chambers asked him about his rape convictions, Rewa said he felt "terrible shame".

"I can understand the hurt that I put on these women," he said.

But, Rewa added, he could also understand the lack of forgiveness from his victims.

"It wasn't something that they could accept, not after what I'd done to them.

"I would never ask them to do that, I can never imagine any one of them forgiving me for what I've done."

Rewa said he had also struggled to forgive himself.

"I never had the strength to do that, I've never had the strength to forgive myself for what I've done.

"You can't forget things like that, that's something that's there all the time ... Every time it's put up on TV I feel the shame of it."

But Rewa said he believed he was now a changed man.

"I like to believe I am," he said.

Chambers' questions then became more pointed.

"What about Susan Burdett? Did you rape and kill her?"

Rewa replied: "No I didn't ... If I was guilty of it, yes I would [say I did that]."

He said it "would be difficult not to, if you were guilty of it".

Burdett, a 39-year-old accounts clerk, was killed in her Auckland home in 1992.

Her bludgeoned body was found by a friend on Wednesday, March 25, 1992.

Rewa, however, said he first met Burdett in 1990 and claimed the pair were in a secret sexual relationship.

He said at the time he was taking cocaine, speed, LSD and occasionally ecstasy.

Sometimes he took ecstasy with Burdett, Rewa said.

"The love drug, it gave you a sense of euphoria."

The weekend before her death, Rewa said Burdett came to his home to enquire about some more pills.

The next time Rewa said he saw her was on the Monday she was killed.

"I was at home. She just turned up," he said.

"I wasn't one for watching TV, but when she came around I was watching TV. The only time I would watch TV was for watching the news."

He said the pair split an ecstasy pill and had sex.

Burdett then went on her way, Rewa said, before he later learned his "friend" had been killed.

"All the years I've been coming to court for this, you know this is my third trial ... Nobody ever asked me about the friendship we had. All they were worried about was finding someone to blame for the murder. She wasn't just Susan Burdett, she was my friend too."

However, under cross-examination, Crown prosecutor Gareth Kayes referred to the transcript of Rewa's second trial and said then prosecutor and now High Court judge Simon Moore asked: "Was it a relationship you valued?"

Kayes then accused Rewa of fabricating a relationship with Burdett.

"Was there a relationship?" The Crown lawyer asked.

Rewa replied: "Yes there was."

"That's a lie isn't it Mr Rewa?" Kayes replied sharply.

"You are making it up to explain how your semen got inside Ms Burdett's dead body," Kayes later said.

Rewa seemingly grew agitated as Kayes continued.

"You know, you've made all of these suggestions," Rewa said.

"I've been tried twice for this ... It pointed to somebody else.

"There are other people involved in this, and all the evidence pointed somewhere else ... There's been two other trials," Rewa proclaimed.

"I didn't punch her, I didn't hurt her, I didn't rape her and I didn't do what you are trying to say."

Kayes alleges Rewa entered Burdett's home on March 23, 1992, and raped and murdered her with a baseball bat.

The prosecutor said the rapist had climbed through Burdett's window and surprised her as she was getting ready for bed.

Chambers, however, has accused Burdett's son Dallas McKay of killing his mum.

McKay was once treated as a suspect by police during the investigation into Burdett's death.

He strenuously denied killing his mother.

Rewa has been convicted of raping several women between 1987 and 1996.

Burdett's killing, Kayes alleged, displayed a "striking resemblance" to Rewa's other sexual assaults.

Teina Pora was twice wrongly convicted for murdering Burdett on the back of a false confession.

He was arrested as a 17-year-old and spent 22 years in prison before the Privy Council quashed his conviction in 2015.

He has since received an apology from the Government and $3.5 million in compensation.

A stay of proceedings for a murder prosecution against Rewa was applied by the Solicitor-General in 1998, but two years ago the Deputy Solicitor-General reversed the stay thus allowing the current trial.

A stay had never before been lifted in New Zealand's legal history.

The trial continues.