Almost 25 years ago to the day, Vicki Cleary was stabbed repeatedly by her former boyfriend, Peter Keogh, outside the kindergarten where she worked. Keogh went to jail for the killing.

He had successfully claimed in court that her behaviour that morning - swearing at him when he approached her outside her workplace, not wanting to resume the relationship - had ''provoked'' him into violence. He was convicted of manslaughter, for which he served less than four years in jail.

Ever since, Cleary has been a tireless campaigner against violence against women and laws that he sees as allowing it to go unrecognised and unpunished.

''It wasn't just that I lost a sister, but I saw the court in its scandalous operation,'' Mr Cleary said. ''We Westerners look at faraway countries and we talk about what the Taliban do to women … we parade our morality as being superior … and yet we let men offer the same excuse for the killing of women.''

Mr Cleary will address the second day of the NSW parliamentary inquiry into provocation, a partial defence that allows murder charges to be reduced to manslaughter in cases where it is established the attacker lost control based on actions or words of the victim. Provocation was abolished in Victoria in 2005 following campaigns from victims' family members, including Mr Cleary, and a damning report from the Victorian Law Reform Commission.

Assistant Police Commissioner Mark Murdoch told the inquiry yesterday it was wrong that words or non-criminal actions like leaving a relationship, or adultery, were still accepted as an excuse for killing someone.

''Words alone should not amount to provocation, no matter the intensity, ferocity or malice,'' he said. ''For goodness sake … I would like to think in the 21st century we are beyond the fact that if adultery occurs in a marriage or between partners, that is not sufficient reason in itself to take someone's life.''

The inquiry was sparked by a recent provocation case in NSW where a man, Chamanjot Singh, slit his wife's throat after she reportedly threatened to leave him and have him deported.

Mr Cleary said he was not calling for provocation to be abolished altogether. Rather, he and Assistant Commissioner Murdoch agree it should only apply where the ''provocative'' conduct was extreme, criminal and/or violent.

''We have to rule out evidence that is at odds with a woman's lawful human rights. You can't use alleged infidelity, you can't use alleged words,'' he said.

''[Women like my sister] are killed because they expressed their independence, and we've got to stop that.''