Monis' partner Amirah Droudis, 37, is on trial for the murder, accused of stabbing the woman 18 times, dousing her in petrol and setting her body on fire in the stairwell of his western Sydney apartment block in 2013.
In his closing submissions, Senior Public Defender Mark Ierace SC said Monis could have contracted the killing of his ex-wife.
Mr Ierace said Monis had taken out $150,000 insurance coverage on his unit where he planned for the murder and fire to occur because he "must have needed to pay a significant sum of money for the killing".
The court heard that Monis had approached members in different chapters of the Rebels outlaw motorcycle gang multiple times asking if they could help him murder his ex-wife.
One gang member said Monis approached him in early 2013 and said he "wanted to have a woman done in and he would pay to have a woman done in" and had also asked about accessing knives and guns.
Mr Ierace said Monis was not someone who had ready access to money, and the insurance was the means he had in mind to pay for the hit. His motorcycle, which was last identified as being registered in Western Australia, was handed over as security.
"Police have been unable to eliminate the direct involvement of outlaw motorcycle gang members in the killing of the deceased," Mr Ierace said.
Both the Crown and Defence agree that Monis was the "mastermind" of the murder of his ex-wife, who can not be named for legal reasons. But the Crown's case is that Ms Droudis was "brainwashed" by Monis and was ready to do whatever he asked of her, including the murder, to ensure their continuing relationship.
Mr Ierace said there were no forensics that linked Ms Droudis to the murder scene, no evidence as to how she supposedly travelled to and from the apartment, and no marks observed on her hands that would have been consistent with a knife struggle with the ex-wife.
Ms Droudis had not been identified in a photographic line-up by any of the eye-witnesses who observed the attacker in daylight and in close quarters and had never confessed to the crime despite seven months of surveillance, the court heard.
Mr Ierace also said that eye-witness accounts that Monis' ex-wife screamed "I have children" as she was being stabbed suggested she thought she was being attacked by someone who did not know her.
In his closing address last week, Crown Prosecutor Mark Tedeschi QC told the court that it was not in dispute that the murder was committed by a woman having been identified as such by all four eye witnesses.
"Your honour could use your knowledge of the world to say that it is most unusual for a male instigator, in this case Mr Monis, to use the services of a hit woman to perpetrate a murder," Mr Tedeschi said.
The defence's closing address is due to continue on Tuesday afternoon.