Last week, 24-year-old Chamanjot Singh was acquitted of murder after brutally killing his wife Manpreet Kaur in December 2009. Despite cutting her throat eight times with a box cutter, Singh was instead found guilty of the lesser crime of manslaughter.

The court heard that Singh had been jealous of the new friendships Manpreet had made since moving here from India, and had beaten her previously.

So why, then, was he found not guilty of murder? Because he argued he was caught in a “triangle of desperation” — Singh believed his wife had been unfaithful, after she had told him she loved another man. He had also overheard a relative of hers earlier in the evening slander his mother in a phone call from India.

In NSW — as well as some other states — the defendant can argue that he was “provoked” into killing. If the defendant can convince the jury that he acted as a “reasonable” person would in response to something the victim said or did, he can be charged with manslaughter instead of murder.

I say “he” deliberately because the provocation is rarely used successfully by women.

The defence is nearly always claimed by men, often in cases where a female partner has cheated on him or threatened to leave. The Victorian Law Reform Commission’s Defences to Homicide Report of 2004 found that from 1997 to 2001, 24 men raised provocation as a defence — 12 of them for killing an intimate partner. Only three women raised provocation, and none were successful.

Notably, it has also been used by men who have killed in response to “gay panic”, where the attacker believed the victim was coming onto him.

Judy Jackson, former Tasmanian attorney-general, told the Tasmanian parliament when introducing a bill to abolish the defence in 2003: “The defence of provocation is gender biased and unjust. The suddenness element of the defence is more reflective of male patterns of aggressive behaviour.”

In 1996, Heather Osland was found guilty of murder in Victoria for killing her abusive husband, who over the years had repeatedly s-xually assaulted, beaten and suffocated her, among other horrific stories. Because she had planned to kill him beforehand, Osland could not claim years of abuse as provocation to kill.

Traditionally, the law has stated that provocation can only be claimed if the homicide occurred “suddenly” after the occurrence of the incident in question. This is certainly the case in NSW, and was in Victoria at the time of Osland’s trial. This stipulation has been shown to favour men, who are more likely to respond violently and immediately in a tense situation.

In Queensland, 28-year-old Damian Sebo was found guilty of manslaughter in 2007 after killing his 16-year-old girlfriend Taryn Hunt. Hunt had taunted Sebo about his s-xual prowess, so he responded by bludgeoning her to death with a steering wheel lock.

In response to the outrage caused by this case, the Queensland government last year legislated against the use of provocation in response to verbal taunts.

Victoria, however, has led the way in law reform around this issue. In 2005 the Bracks government replaced provocation in the Crimes (Homicide) Act 2005 with “defensive homicide” — popularly known as the “battered wife law” — which makes it harder for men who kill their female partners — and easier for victims of family violence — to argue for a reduced conviction.

Like in Queensland, Victoria’s change in laws was in response to an incident that horrified the public — namely the case of James Ramage, who was found guilty of manslaughter after killing his wife Julie, because she had left him for another man.

One key reform that was recommended by the Queensland Law Reform Commission report on this topic is to shift the burden of proof onto the defence to prove provocation. Formerly it was up to the prosecution to disprove beyond reasonable doubt that the attacker was provoked — a difficult task when the only other witness to the crime is usually the victim. Queensland has since legislated to shift the burden of proof onto the defence; NSW has not.

In most jurisdictions in Australia, the magistrate can take any mitigating factors into account during sentencing, meaning any extenuating circumstances to be dealt with then. In Queensland, however, this is not the case, as mandatory sentencing for murder leads most lawyers to recommending provocation be retained.

Victoria, Tasmania and Western Australia have abolished provocation entirely. Australia’s other states and territories, however, still have some version of the defence on the books. As Jackson told the Tasmanian parliament:

“The defence was not designed for women and it is argued that it is not an appropriate defence for those who fall into the ‘battered women syndrome’. It is better to abolish the defence than to try to make a fictitious attempt to distort its operation to accommodate the gender behavioural differences.”