Joanne Dennehy's sister Maria on triple killer's childhood

The bright and bookish school girl who would grow up to murder three men

Joanne Dennehy, who killed three men and attacked two others, has become one of the UK's most notorious killers. But the sister Maria Dennehy knew as a child was bright, happy and bookish. What went wrong?

Their lives could not have not have followed more different paths.

While the younger sister Maria was forging a successful career in the Army, during which she served in Afghanistan, Joanne Dennehy was mired in a world of drink, drugs and self-harm.

She emerged from this world to murder three men and try to kill two more, leaving her family wondering how she had changed so much?

"Parents always blame themselves, but they were a great mum and dad," said Maria.

"Our parents were hard-working. My dad worked for BT at that time and mum worked at a supermarket and they worked very long hours.

"We were very spoilt as children, always on holiday.

"My parents gave her a good education. She was very academic and used to read books and liked to learn a lot of stuff."

Asked if there was any evidence of violent behaviour, she replied: "No, absolutely nothing."

But that does not mean everything was perfect in the Dennehy household. It was not.

When Maria was about 11 years old, the 13-year-old Joanne ran away from home for the first time.

Joanne Dennehy with a girl who cannot be identified and a teddy that was given to Dennehy by the girl

Joanne had met a young man at football match. Maria believes he was aged 18 or 19 at the time.

When her parents found out, said Maria, "they put a stop to it straightaway".

"In anyone's eyes it's not right for an 18-year-old to look at a 13-year-old girl.

"They ran away together and were found in Milton Keynes in a hostel."

Her parents brought her back to the family home in Harpenden only for her to run away, again and again. And Joanne started stealing from her parents.

But much of what was going on was unknown to the young Maria as her parents "kept me away from a lot of her behaviour".

The last time Joanne ran away was when she was 15.

She did not see her sister again until seven years later when Maria made contact again after getting engaged.

"I wanted to find her, to ask her why she left the family," she said.

"I found her through the electoral roll, she was living in Cambridge.

Maria Dennehy said her older sister 'liked to learn a lot of stuff' and was 'very academic' as a young girl

"I went round and she answered the door and I saw the state of her.

"She was self-harming and doing drugs.

"She had two kids, the youngest was about six or seven. She asked for money for the kids and I refused to give her any.

"That was the last time I physically saw her."

Maria remained in occasional contact via the internet.

"She was still getting herself in trouble. She said she was bi-polar, which was a complete lie.

"She wanted to believe in it, to justify what she was doing. There were lots of lies, I never knew what to believe."

Maria's observations about her sister's lies are consistent with the findings of psychiatrists.

More than a year before she murdered John Chapman, Lukasz Slaboszewski and Kevin Lee, Joanne was admitted to a psychiatric ward at Peterborough City Hospital.

She stayed in the unit for three days. Subsequent assessments by psychiatrists have found she has a psychopathic disorder.

The jury in the trial of Dennehy's accomplices, Gary Stretch and Leslie Layton, were told by prosecutor Andrew Jackson the disorder involved traits such as "superficial charm, a disregard for others, pathological lying and a capacity for showing no remorse, to exaggerate and lie".

She was also found to be emotionally unstable and prone to unpredictable behavioural explosions.

What happened last spring was a 10-day explosion - one that blew apart the lives not only of her victims, their friends and their families, but of her own estranged family too.

"What she has done and is, I can never come to terms with that," said Maria.

"I've got a young child and my mum will say 'you and Joanne used to do that'.

"It's very hard."