An Australian court has dismissed an appeal by Erin Patterson, dubbed the “mushroom murderer,” against her conviction and ruled that she should spend the rest of her life behind bars without the possibility of parole. The decision was delivered on Friday by a three-judge panel at the Supreme Court of Victoria.

Patterson was convicted last year for murdering three relatives of her estranged husband with a meal laced with deadly death cap mushrooms. The conviction also included the attempted murder of a fourth guest who survived.

"This offending was extraordinarily cold and calculated, and stands to be denounced in the strongest terms," Justice Stephen McLeish stated on behalf of the panel. "In all the circumstances, after anxious consideration, we have concluded that the case involved such shocking criminality that it is inappropriate to fix a non-parole period."

The court's ruling means Patterson will not have the chance of parole, effectively condemning her to life in prison. Her crimes involved an "elaborate series of deceptions," including falsely claiming a cancer diagnosis to explain why her two children were absent from the fatal lunch, the judge noted.

Patterson, then 51, was found guilty of murdering Gail and Donald Patterson, and Gail’s sister, Heather Wilkinson, by serving them a beef wellington dish contaminated with the poisonous mushrooms. Heather’s husband, Ian Wilkinson, was the sole survivor of the meal.

She had been sentenced to life in prison with a 33-year non-parole period, one of the longest terms ever imposed on a woman in Australia. Patterson has consistently denied wrongdoing, maintaining the deaths were accidental. Her legal team argued that certain evidence should not have been presented at trial, that her cross-examination was unfair, and that jury's accommodation arrangements compromised the verdict.

Judges determined these grounds for appeal were insufficient. Patterson's final legal recourse is to apply to Australia’s High Court to challenge her sentence and convictions.

Patterson is only the second woman in Australia to be sentenced to life imprisonment without the possibility of parole. The first was Katherine Knight, who received the sentence in 2001 for a murder committed in 2000.