The teenage dominatrix convicted and then acquitted of murdering Peter Plumley-Walker has spoken of her regret at not calling 111 after finding the cricket umpire unconscious and not breathing during a bondage session.

Renee Chignell was 18 when Plumley-Walker died after attending a $200 bondage session with her in January 1989.

Chignell and her then boyfriend Neville Walker – who both later dumped Plumley-Walker's body off the Huka Falls – later faced three murder trials over the death. They were convicted at the first trial, the jury at a second trial ordered on appeal couldn't reach a verdict, and the pair were acquitted at a third trial.

The crown claimed Plumley-Walker was still breathing when thrown off the Huka Falls. But the jury in the latter trial agreed that the 51-year-old had died accidentally during the bondage session.

Peter Plumley-Walker. (Photo / Supplied)

Chignell, now 47, has opened up on the case that shocked the country in the docu-drama, Mistress, Mercy - The Renee Chignell Story, broadcast on TVNZ 1 tonight.

In it, Chignell has spoken of her horror at seeing Plumley-Walker – who was chained up - in distress after checking on him during a break in the session.

"I can't even put words into how I felt when I saw him," she said in Mistress, Mercy - The Renee Chignell Story.

"I remember screaming out to Neville. He came in. I was getting him down on to the floor."

But she says it was Walker's decision to not call for medical help.

"I insisted to Neville that we phone the ambulance ... this man needed help ... he definitely needed help," Chignell said.

"Neville was trying to help with the chest compressions.

"If I could turn everything back, by God we would have been on the phone straight away. I don't understand why I listened. It's my fault as well for just not doing what I knew was the right thing to do, picking up the phone and ringing the ambulance."

Plumley-Walker had booked the bondage session at Chignell's Remuera townhouse, where she lived with Walker and where they ran the sessions, on the day his divorce was settled.

Neville Walker. (Photo / Supplied)

Chignell described her client as "very pleasant. Very polite ... a gentleman."

She said Plumley-Walker told her he had been "naughty" and "needed to be disciplined".

Before the session, Plumley-Walker was told to say: "mercy, mistress mercy" as a safe phrase to end the session.

"I would say: 'Slave, I'm going out of the room, you're to behave, you know I will be back soon," Chignell said.

"And I would sometimes go out, sometimes not, I would open the door, shut the door, still be there and then come up and give him a smack. And it's just that, that heightened sense of arousal that they're going through."

She said there was nothing to suggest Plumley-Walker was struggling with the session or his health.

But after returning to see him after taking a break she discovered him unconscious and not breathing.

"I would have thought that if he was having any problems he would have yelled out or made some noise," she said.

"I would have heard the chains shaking ... they were down and would have made a noise if he was trying to get my attention."

Chignell and Walker put Plumley-Walker's body in the boot of his car and drove it to the Huka Falls, near Taupo.

"The next thing I knew that we were in the car driving down," Chignell said of the journey from Auckland to Taupo.

"I remember a lot of crying. Just being so overwhelmed with the whole situation. It just being so surreal that this was ... it was just far too much going on to really take on board the enormity of the situation."

Once at Huka Falls they hurled the cricket umpire into the surging water.

Plumley-Walker's body was found several days later, and the police launched a major operation that left the country shocked and enthralled.

Manon Blackman as Renee Chignell in Mistress Mercy. (Photo / Supplied)

In the docu-drama, Chignell recalled hearing the guilty verdict at the first trial in 1989: "I can hear my mother calling out to me, telling me that she loves me.

"That was [a] really, really painful memory to just, just to feel the hurt ... from family and friends. That will stay with me for a long time."

At the third trial in mid-1991, when Chignell and Walker were finally acquitted, Chignell remembered "just being so thankful, so thankful".

"It was wonderful. It was just that life could start again."

Mistress, Mercy - The Renee Chignell Story received more than $1 million from NZ On Air and has been produced by the Gibson Group.

It also features interviews with Chignell's lawyer, Stuart Grieve, QC. Actress Manon Blackman plays Chignell in dramatised sections of the show.

"This case has been one of the big ones in New Zealand history, and it just seems like it doesn't sort of go away," Chignell said.

"I was there so I know what happened. I was very naive, very young, very stupid."

Mistress, Mercy – The Renee Chignell Story is on TVNZ 1 tonight, 8.30pm, as part of the Sunday Theatre season.