How Joanna Dennehy went from an innocent child to one of Britain's most dangerous serial killers

How Joanna Dennehy went from an innocent child to one of Britain's most dangerous serial killers

Notorious serial killer Joanna Dennehy had a very normal childhood, it turns out, but it was one that quickly turned out horrific after she became a teen. In ITV's documentary 'Joanna Dennehy: Serial Killer', her sister Maria talked about how the older sister she looked up to turned into a monster. A picture of the sisters that was taken when they were children, Joanna at the age of six and Maria when she was four, showed the innocence in the now killer's eyes.

The contrast that they both have stemmed from the lives they led that took very different paths. Maria joined the army while Joanna led a life of drugs and extreme violence which ended in her becoming one of England's few women serial killers. Maria spoke to 'Good Morning Britain's Susanna Reid in the documentary and gave her insight into what made her once-talented sister turn into a cold-blooded killer.

Maria (L) with her sister Joanna (Source: YouTube)

Joanna had once described that she had been physically abused as a child and that her parents were not very caring but Maria said otherwise. The devastated sister has been convinced for a long time that it was excessive use of cannabis and other drugs in Joanna's early teen years that led to her immense rage and caused her killing spree. She said in a 2014 interview: "I don’t know what else could have caused such a radical change in her personality from age 14."

Maria said in the interview that her older sister was always strong-willed and was a rebel by nature but it was after she started mixing with a gang of older drug-using boys that her personality changed. Before this radical change, the sisters had shared a room and even had a secret language.

The war veteran said: "She was my big sister and I really looked up to her. At junior school, she was very protective and if anyone was horrible to me, she would step in and tell them off. Once, when she was about seven, she made a bigger boy apologize for calling me a nasty name in the playground. We did a lot of sporty things together. She even made up a secret language that we used all the time. There was a deep bond between us. Although I was younger, she always had time for me – we shared all our secrets with each other. But my favorite memories are of the times that she would make up lyrics to songs and teach them to me."


Joanna as a young girl in school (Source: YouTube)

Maria said in the interview that the carefree nature the sisters had in their childhood changed completely when Joanna met John Treanor, a local boy who was five years older to Joanna. She went on to say that her sister became cold and distant at that point. She said: "She dropped not only her old neighborhood friends but started to see me as a nuisance. I think she was excited by her lifestyle. I don’t believe it has anything to do with the way we were brought up. We both had the same treatment, the  same opportunities."

Joanna was the "bright daughter" for their parents and was supposed to make the family proud by becoming a lawyer. Maria said: "Our parents were very protective of us. Perhaps they were a little too strict, but we were not beaten or abused in any way. They treated us the same, but it was Joanna who rebelled. No one can understand what went wrong."


In their early years, Maria said that Joanna was the quiet, sweet "girlie girl" who loved to dress up and play with dolls. She was never aggressive and was a well-behaved child compared to her outspoken younger sister. Maria continued: "Everyone is speculating about why she turned out the way she did. I think the people, the drugs and the environment she went into triggered something dark inside her."

Joanna shortly before she ran away from home with John Treanor (Source: YouTube)

The furious sister didn't want to blame John for bringing about the change in her sister, who has since painted himself as the victim of Joanna's excesses. The couple were together for 14 years and even had two children together before Joanna showed her true colors.

MEA WorldWide (MEAWW) previously reported that, in March 2013, Cambridgeshire found itself in the limelight after a series of murders rocked the United Kingdom. The crimes were referred to as the "Peterborough ditch murders" as the three victims of the horrific crimes — all males who died of stab wounds — were found dumped unceremoniously in ditches outside Peterborough. The murderer was later discovered to be Joanna, who has come to be known as "the most dangerous woman in the prison system".


Joanna had reportedly hunted and stabbed the men for the sake of entertainment. She told Gary Stretch, who was formerly known as Gary Richards and was her alleged accomplice: "I want my fun. I need you to get my fun."  She told a psychiatrist at a later date that she found the act of murder to be "moreish" and that, after she killed for the first time, she "got a taste for it".

Joanna Dennehy (Source: YouTube)

Maria was not the least bit surprised that she had entered a guilty plea and said in an interview: "I think she did that to control the situation. She likes people to know she's the boss." Joanna is still being held at HM Prison Bronzefield. Assessing psychiatrists later diagnosed the killer with psychopathic, anti-social and borderline personality disorders.


'Joanna Dennehy: Serial Killer' premiered on ITV on April 18 this year

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