Siege gunman's ex guilty of murder

The ex-girlfriend of Lindt cafe gunman Man Haron Monis has been found guilty of murdering his ex-wife in a "hot blooded and frenzied" attack.

Amirah Droudis' twisted obsession with Monis has left her facing a long stint behind bars after she was convicted of murdering the 30-year-old woman outside a Sydney unit in April 2013.

The 37-year-old was found guilty on Thursday of stabbing Monis' ex-wife 18 times, dousing her with petrol and setting her alight at a Werrington apartment block in Sydney's west.

In handing down his verdict, Supreme Court Justice Peter Johnson said Droudis had become "enthralled" by Monis, who took advantage of her willingness to act at his behest.

"This was a hot-blooded and frenzied murder by an enraged female attacker," he said in his judgment.

"This crime had all the hallmarks of a frenzied attack by an angry amateur killer, acting in a manner consistent with Monis' desire."

At Droudis' judge-alone trial, her defence team suggested the assailant could have been another woman or a hired bikie killer.

But Justice Johnson rejected the theories as fanciful and inconsistent with the evidence.

Droudis stood in the dock and showed no emotion at the verdict.

She is due to face a sentence hearing on November 30.