Kathryn has interviewed more than a hundred female murderers. They often have one thing in common.

Twenty years ago, when criminologist Dr Kathryn M. Whiteley decided to focus her research on female murderers, she was scoffed at.

"Why bother putting so much time and effort into such a small cohort of the criminal population?" she was asked.

"What can we gain? What can we learn?" she was pressed.

Female killers are rare, after all. They account for only 10 per cent of total homicides across Australia, Canada, England and the US.

Watch: Kathryn spends a lot of time with female killers. Post continues below.

But Dr Whitelely was adamant.

She travelled from her native Queensland to the notorious Dame Phyllis Frost Centre in Victoria — a maximum security prison for women — as it was the only Australian facility that would allow her access.

Once there, she realised she had her work cut out for her.

"I kept getting reminded by the women, 'If you want to know about or why I committed the crime, you really need to understand who we are,'" she recalled to Mamamia's True Crime Conversations.

"So it really was a changing moment for me, because I went from my research agenda of wanting to talk to women about their criminality, to wanting to get to know them."

Even on the surface, the statistics around female killers are sobering.

Here in Australia, Whiteley's research shows the cohort consists of largely ethnic minorities in the 20-24 year age bracket. A majority have socio-economic handicaps, many are single mums, and there's regularly substance abuse, mental health issues or a history of sexual abuse mixed into their histories.

In an effort to study a higher concentration of women who kill, Whiteley moved to the United States and has spent a large chunk of the last two decades interviewing and getting to know prisoners at SCI Muncy, a maximum-security facility for female offenders in Pennsylvania.

Over time, she's noticed a common theme.

"Often it is a first time crime. They don't have any history," she told True Crime Conversations.

Listen to the full conversation with Kathryn M. Whiteley. Post continues below.

She's also noticed that the number of women who have had adverse childhood experiences is extremely high.

"They were victimised by neglect, abuse, sexual, emotional and physical abuse," she explained.

Whiteley estimates that 70 per cent of the hundreds of women she's spoken to have expressed remorse for their crime, and her research has shown that women who commit a violent crime, if they are released, never re-enter the system.

"For men it's different… it's a lot higher. It could be up to 60-65 per cent [re-offend] if they have committed a violent crime," she said.

Another difference she's noticed between the sexes is that women kill someone close to them the majority of the time. Someone they know.

But with men, "a stranger acquaintance is more likely," which is surprising when you consider that in Australia, at least, men are also killing an intimate partner on average once a week.

Meet the women serving life.

Whiteley considers many of the women serving life without parole in SCI Muncy friends, despite the horrific things they've been sentenced for.

Marilyn Dobrolenski was 19 and looking at the death penalty when she went on trial for the murder of two police officers in Delaware in 1972.

She ended up getting a life sentence, and has been behind bars for 52 years.

Her childhood was filled with sexual and physical abuse, teen pregnancy and getting mixed up with a bad man who ended up being her co-accomplice in the double murder.

Image: Delaware County Daily Times/Newspapers.com.

As Whiteley told True Crime Conversations, "It's very interesting when you listen to her talk, what she basically says is that prison, a State Correctional Facility, gave her a new life — gave her life in general."

Then there's Terri-Joell Harper, a 22-year-old serving Philadelphia police officer who was sentenced to life without parole in 1993 for assisting her then-boyfriend in the shooting murder of a businessman who apparently owed him a debt.

She's also been behind bars for several decades now.

"She has remorse… she's never getting out. She's come before the Board of Parole twice and has been denied. She was gutted," said Whiteley.

Jamie Silvonek entered the system when she was 14, charged with the murder of her mother in 2015 because she didn't approve of her relationship with her 20-year-old boyfriend. Tried as an adult, Silvonek was accused of being the mastermind behind a plot Caleb Barnes carried out.

Sentenced to 35 years, Silvonek told Whiteley her memories of the murder and her early days in prison are a "blur".

"I was a monster," 14-year-old Jamie Silvonek said in court after killing her mother.https://t.co/jjE6dLXHcW pic.twitter.com/QMbaK6xIxj

— KFVS News (@kfvsnews) February 14, 2016

As a juvenile in an adult prison, she was segregated for many years and has "excelled academically" since being allowed into general population.

"She talks about how unexpectedly she still has the love and support of her family, considering she took something so valuable from them," Whiteley told True Crime Conversations.

Despite the horrible things these women have done, Whiteley doesn't feel any fear or anxiety stepping inside the walls of SCI Muncy.

"When I talk to them, I'm not looking at the crime. I'm wanting to know more about this woman sitting opposite me," she said.

"I do have a wonderful time engaging with the women."

That being said, Whiteley admits there's "certainly a cohort of women that do choose to be bad, that are evil. But there are some women that certainly aren't."

"There are women there in my heart that I believe should not have received life. Understanding their background and understanding behind-the-scenes [of] the criminality… I would honestly say that they should not be serving life without parole.

"There are women in the United States — if you were to parallel the criminality of the crime in Australia — the women in the United States, well and truly, would have been released by now," Whiteley told True Crime Conversations.

Given the severe lack of research and time spent understanding female killers, Whiteley has dedicated her career to making sure their voices are heard.

In her eyes, they are more than the "monster" and "evil woman" the media portray them to be.

She's determined to show us why.

Feature image: Getty