Former attorney-general Jim McGinty has joined a campaign for a judicial review of the cases of two women serving life sentences in Bandyup Prison for murdering their husbands.
Killers Robyn Buller and Lesley Dowling were victims of domestic violence who posed no threat to society if they were released, Mr McGinty said.
They were convicted and sentenced before a 2008 amendment to the Homicide Act, enacted while Mr McGinty was attorney-general, which instructed courts to take into account histories of domestic violence.
"The law has changed fundamentally and women who've killed their husbands who may not have been found guilty or certainly as severely punished deserve to have their cases reviewed," he said.
"It could make a significant difference, both as to guilt or otherwise and certainly as to penalty, taking into account the very significant change to the law as was recommended by the Law Reform Commission.
"I think it is wrong to not allow these women to be able to present their case back to the court."
Mr McGinty will speak at a rally at Parliament House today organised by the Social Justice Alliance, which is petitioning for MPs to intervene after Attorney-General Michael Mischin rejected petitions on behalf of the women.
Mr Mischin recently considered the cases and disagreed the 2008 amendments would have resulted in acquittals or lesser sentences.
He said Buller, jailed over the shooting of her husband David in 1999, had planned and concealed the crime to a significant degree.
In the case of Dowling, convicted of wilful murder along with her teenage son Marcus Pitts for the 1994 killing of husband Neil, Justice Terry Walsh made it clear the crime was a serious one that called for a long sentence.
He commented when sentencing Dowling that the circumstances were "extremely grave" and "probably as bad a case of murder as one would normally come into contact with".
The families of the women's victims could not be contacted.