An internal police report into the bashing death of a Perth woman has cast doubt on whether she was killed by a single blow.

The claim was a significant factor in the decision to use a controversial charge that critics later attacked as too lenient.

In September 2011, the WA Supreme Court heard that mother-of-two Saori Jones died after being punched by her partner, Bradley Wayne Jones.

Jones received a five-year jail term, but will be eligible for parole in December 2013.

The prosecution and the court accepted evidence given by Jones that he only recalled hitting his wife once.

Jones faced the lesser charge of unlawful assault causing death, in part because of this crucial admission.

The charge attracted a maximum 10-year sentence in contrast to manslaughter, which can lead to up to 20 years' jail.

An internal police review, obtained by the ABC's Four Corners program following a freedom of information application, shows police were told Ms Jones may have died following "repeat blows", calling into question Jones's claims.

The police report does not disclose where this evidence came from.

The heavily redacted report was obtained by Four Corners following the screening of A Matter Of Life And Death in June.

Jones, a martial arts enthusiast, admitted to punching his partner in the head, knocking her to fall to the floor, where she lost consciousness, in December 2010.

He left her body to decompose for 12 days at his home, which he was sharing with his two young children.

Ms Jones had been staying in a domestic violence refuge at the time. Her disappearance led refuge workers to make frantic calls to police, who initially accepted Jones's claims that Ms Jones had run off with the best man from their wedding.

When officers found Ms Jones, her body was so badly decomposed that the precise cause of death could not be medically determined.

The charge of unlawful assault causing death, that was used to convict Jones, was originally designed to address one-punch deaths resulting from pub fights. Jones later claimed he only clearly remembered "punching the victim once".

The report obtained by Four Corners also shows police were aware of at least four earlier violent incidents leading up to the death, including one when Jones allegedly hit Ms Jones and banged her head against boxes while hurling abuse. Jones was charged with aggravated common assault in connection with the incident.

It also raises questions why Jones's claim, that he only recalled striking his wife once, went unchallenged.

WA Police declined to respond to questions.

'No sufficient evidence'

WA Attorney-General Michael Mischin said prosecutors had to rely on Jones's version of events because they could not establish a causal link between the assault and the death.

"There was no sufficient evidence that Bradley Jones intended to kill Ms Jones or intended to do her any life-threatening or health-endangering injury," he said.

He defended prosecutors and said the decision would have been made on the available evidence.

"If the evidence is not sufficient to sustain a murder or manslaughter charge, then it will fail and it is irresponsible to charge people with offences unless there is a reasonable prospect of convicting them for it," he said.

"As a matter of practice, the director of public prosecutions will always charge the most serious offence open on the evidence."

Since Ms Jones's death, WA's Labor Opposition has sought to increase the maximum sentence for unlawful assault causing death in domestic violence cases - an amendment known as Saori's Law.

The Barnett Government, however, blocked the amendment in October.

Angela Hartwig, chief executive of the Women's Council For Domestic and Family Violence Services, said she was disgusted by the Government's decision.

"Saori was not a passive victim in the violence," she said.

"When you find out the whole story, she made contact with the refuge, she made contact with the Japanese [support] group, she actively took steps to resist the violence."

The police review also revealed that Ms Jones wanted to take her children to Japan – a decision police believed may have triggered Ms Jones's death.

"To put it bluntly, the word is out that you... can kill your partner, where there is a history of domestic violence," Ms Hartwig said.

"It doesn't deliver justice to the victims and their families."

Ms Hartwig said domestic violence deaths have more than doubled, reaching 22, during the past 12 months. Almost half of all victims were aged under 30.

Family violence campaigners gathered in Perth yesterday to remember the victims of family violence and promote awareness of the issue.