When women go against their traditional nurturing and care-giving qualities and commit acts of pure evil, we find it difficult to believe that these wives, mums and daughters could be so depraved.
Yet every year in Australia – and around the world – women carry out around 15 per cent of murders, many of which are calculated and premeditated. Queensland University of Technology researcher Dr Belinda Parker, who examined the motivations of 149 female and male killers for her thesis Seven Deadly Sins, says there are definable reasons why people kill.
"The seven homicide event motives include revenge, jealousy, thrill, love, gain, conviction/hate and concealment (to cover up another crime)," she says.
While attending Mulawa Correctional Centre in Sydney's Silverwater, forensic psychologist Marcelo Rodriguez has observed violent female offenders at close quarters and agrees they are unlikely to act on impulse.
"A lot of women plan it," he tells Woman's Day. "They know what they are doing."
Years of physical and mental torture push female offenders to the brink, he says.
"They don't turn dangerous overnight. Sadly, they are very damaged and have very unfortunate backgrounds of child abuse or physical neglect that have caused a personality disorder."
Dr Rodriguez says there's little hope these women will be able to turn their lives around.
"There is no cure," he says. "How can you cure what's happened to them as children and manifested in these horrible crimes?"
Known as Australia's Hannibal Lecter, cannibal Katherine Mary Knight, an abattoir worker and mother-of-four, was found guilty in 2001 of stabbing her partner, miner John Price, 37 times with a butcher's knife.
She had skinned him, put his body on a meat hook in the living room and cooked his head and other body parts into a grisly human stew.
by John's worried co-workers, police found a comatose Knight next to her partner's headless corpse in their NSW Hunter Valley house. Before trying to kill herself, Knight had half-finished a bowl of the stew and left place names of Price's adult children next to other prepared plates.
In an Australian first, Knight, who had a history of sadistic violence towards other men in her past, was sentenced to life without parole. An appeal was rejected with Justice Peter McClellan saying, "This was an appalling crime, almost beyond contemplation in a civilised society."
Knight remains in Silverwater Women's Correctional Centre where she's known as "Nanna".
Belinda van Krevel
In 2000, criminal mastermind Belinda van Krevel lay in bed with her two-year-old daughter listening to her father Jack van Krevel being hacked to death by her lover Keith Schreiber.
She had offered Schreiber $2000 to kill her dad, who she claimed had been molesting her daughter. Leaving a window open, she also planted the murder weapons – a knife, tomahawk and fire poker – for Schreiber, who struck his sleeping victim 25 times and stabbed him 16 times.
Schreiber had been implicated two years earlier in the mutilation murders of alleged paedophile and former Wollongong mayor Frank Arkell and shopkeeper David O'Hearn.
Schreiber's best friend, Belinda's brother Mark Valera, confessed to the killings and became the youngest person in the state to be jailed for life.
Justice Peter Hidden described Jack van Krevel's murder as "the most brutal killing" and said Schreiber's actions were to a significant degree the result of his girlfriend's influence.
Belinda van Krevel pleaded guilty to her involvement and was sentenced to six years in jail.
WATCH: Belinda van Krevel on 60 Minutes. Post continues after video...
Her prison file is marked "too dangerous to be released" and killer Rebecca Butterfield, 43, has done nothing to dispel her jailhouse reputation as the most feared inmate in Australia.
First jailed at the age of 21 for drug offenses, unlawful entry and malicious damage, Butterfield was on parole when she stabbed a neighbour who was trying to stop her from self-harming.
Given a three-year sentence for that crime, she became obsessed with another prisoner, Bluce Lim Ward, eventually stabbing her 33 times. Butterfield was sentenced to a further 12 years for manslaughter, and her mania continued with a string of assaults on other prisoners and staff. She also cut her own throat four times and cracked open her skull by headbutting a wall 105 times.
She was due for release in 2016 but was given an extra five years because of her violent ways. She is now shuttled between two high-security prisons to give guards some respite.
Teen lovers Alo-Bridget Namoa and Sameh Bayda wanted to be Australia's jihadi Bonnie and Clyde and planned a New Year's Eve terrorist attack in Sydney for the day after they were married in 2015.
Believing they had a religious obligation to attack non-believers, the pair's phones included images of soldiers carrying Islamic flags and videos of beheadings. It also had selfies of the couple giving the one-fingered IS salute.
Prosecutor Nicholas Robinson QC told the NSW Supreme Court, Bayda, who had been researching ways to use an improvised device, an incendiary device or a bladed weapon to kill, "was out in the city dressed as jihadi, looking for a target".
Namoa feared her husband would die and wrote him a farewell note saying she would rather die with "a bullet between her eyes" than turn on him.
Meanwhile, Bayda had given his bride a hunting knife and black Shahada flag as a symbol of their murderous plan. A jury found them guilty of their terrorist plot in October 2018.
Jemma Lilley and Trudi Lenon
Murderer Jemma Lilley had an indecent obsession with serial killers and a life-long lust for blood.
Lilley had written a book about a serial killer and later assumed the fictional identity, vowing to tick murder off her "bucket list" by the time she was 25.
Living with a willing accomplice, mother-of-three Trudi Lenon, in a suburban Perth house they called "Elm Street", they hatched a despicable plan.
In June 2016, they lured Aaron Pajich, 18, an autistic friend of Lenon's son, to his death. After first attempting to garrotte Pajich, Lilley killed the teen by stabbing him three times.
Burying Pajich in their backyard, the pair sent each other boasting texts, with Lilley claiming she felt "incredibly empowered".
At the house, police found a bone saw, bleach and a 100-litre barrel of hydrochloric acid.
Sentencing them to life imprisonment, Justice Hall said their crime was "morally repugnant" and, although they blamed each other, they were equally responsible.
Lilley and Lenon were sentenced to life in prison.
WATCH: Jemma Lilley and Trudi Lenon murder Aaron Pajich. Post continues after video...
Mother-of-three Rachel Pfitzner was fed up with the "clinginess" of her two-year-old son Dean Shillingsworth so she choked the boy, wrapped him in plastic and put him in a tartan suitcase.
On October 11, 2007, Pfitzner threw the suitcase into a duck pond in Sydney's south-west, watching it sink before walking away.
The same day, DOCs had sought a warrant for the boy to be placed in the custody of his paternal grandmother. The warrant was served to Pfitzner a week later and she told police her son was already in the custody of DOCs.
When this was proved untrue, further questioning led to Pfitzner being charged with the boy's murder.
Local children made the gruesome find of the boy's body in the pond and the community came together in collective grief and anger.
Justice McClellan found Pfitzner had "manifested a callous disregard for her son" and sentenced her to 25-and-a-half-years in jail.
In 2009, gangland widow Judy Moran ordered the murder of her brother-in-law Des "Tuppence" Moran and drove the getaway car for his killer, gunman Geoffrey "Nutts" Armour.
Judge Lex Lasry accepted the former showgirl and matriarch of a notorious Melbourne crime family had been traumatised by the shooting deaths of two husbands and two sons but this did not excuse the "deliberate killing" of Des Moran, who was shot seven times at an inner city cafe.
Though admitting she didn't like Des, who had once smashed a bottle over her head, Judy protested her innocence, saying she had been polishing the angels on her son Mark's grave when the killing happened.
However, a police surveillance team had watched her dump the getaway car and prosecutors proved she had stashed the gun, a beanie, a wig and a jacket worn by Armour in a hidden safe. In 2011, Judy, now 73, was sentenced to a maximum 26 years in jail.