Serial criminal Malcolm George Chaston has told the family of a woman he killed that if the roles were reversed, he would want the killer dead.

But in a letter he wrote to the family of Christchurch mother Vanessa Pickering, he denies he set out to kill her when he picked her up and drove her to a remote rural area and attacked her so brutally that he broke the handle off a serrated knife.

"She was my work colleague and also my friend," Chaston wrote.

Miss Pickering's mother, Rachel Kitson, told the Herald that the letter meant nothing to her. "It just makes me angry."

Chaston, 41, killed Miss Pickering, 27, on the same day in February last year that he sexually attacked two other people.

He was on bail at the time, and had a history of 71 previous crimes including rape and assault.

Before Miss Pickering's murder, he allegedly boasted in prison that when he got out he was going to hurt and kill women and become famous.

Last month, he was given an open-ended jail sentence, preventive detention, for his crimes, with a minimum 20-year term for killing Miss Pickering.

"I fully understand that no matter what I say, it will not change what I have done and bring back what you have lost," Chaston wrote to Miss Pickering's family.

"I am not saying this to lessen the sentence of the crimes I have committed. I will accept all punishment that's coming to me.

"The anger you feel for me, I understand, for if the role was reversed, I would want the person responsible to live no more.

"Despite what the police have indicated, I had no intention of harming Vanessa.

"I am so deeply ashamed and sorry for my actions, and the pain and suffering I have caused to everyone involved."

Ms Kitson said Chaston's claim he did not mean to kill her daughter was impossible to believe when he took a knife with him to meet her.

She rejected any of his claims of remorse. "He was out on a mission."

She hoped the publicity about Chaston's crime would help prevent other families suffering what her family had.

One of the victims of Chaston's sex attacks told a court at his sentencing that she was thankful to be alive, but still thought about her ordeal every day.

"I hope Malcolm never gets to see the sun again."