My sweet sister the serial killer: One of these girls would grow up a murderer Joanna Dennehy fatally stabbed three men and attempted to kill two more 31-year-old knifed Kevin Lee, Lukasz Slaboszewski and John Chapman Dogwalkers Robin Bereza and John Rogers survived the attack Younger sister Maria says cannabis and skunk use led to Joanna's rampage Siblings had been so close as children they even shared secret language 'Bright' Joanna had been expected to grow up to become a lawyer Maria says her sister changed when she met a gang of drug-smoking boys Neither Maria nor her parents have seen Joanna since her arrest By Angella Johnson Cuddling close, two smiling sisters, one blonde, one dark, pose for a primary school photograph. Joanna, six, curls a protective arm around her four-year-old baby sister Maria. Taken 25 years ago, it is an enchanting image of two little girls united in innocence; the sort of portrait that graces the mantelpieces of homes all across the land. But today the contrast between the sisters" lives could not be more marked. Blonde Maria joined the Army and proudly fought for her country in Afghanistan. Joanna chose a sordid life of drugs and violence which culminated in her killing for kicks, becoming one of Britain's few women serial killers. When a grinning Joanna Dennehy, 31, boasted in the dock at the Old Bailey last November of fatally stabbing three men and attempting to kill two more, the courtroom - and the country - were repulsed and deeply confused. Both sisters had been brought up by loving Home Counties parents who lavished care and affection on them. Yet Joanna brutally knifed her landlord Kevin Lee, 48, Lukasz Slaboszewski, 31, and her housemate John Chapman, 56, then callously dumped their bodies in stinking, water-filled ditches. Sisters: Joanna Dennehy, six, curls a protective arm around her four-year-old baby sister Maria. Maria joined the Army and proudly fought for her country, while Joanna chose a sordid life of drugs and violence which culminated in her becoming one of Britain¿s few women serial killers The killings last March occurred after Mr Lee served an eviction notice on Joanna. She is said to have enjoyed the experience of killing so much she went on a violent spree, randomly selecting and repeatedly stabbing two strangers, Robin Bereza and John Rogers, as they walked their dogs in Hereford. They survived the attack. As the trial draws to an end for Joanna's alleged accomplices Gary "Stretch" Richards and Leslie Layton, who deny helping to dispose of the bodies, Maria, 29, has given a disturbing insight into the demons she believes destroyed her talented sister. Joanna, who described her killing spree as "fun" and posed for photographs clutching a large serrated knife, claimed she had been physically abused at home and indicated her parents were less than caring. Her sister insists this is far from the truth. In fact, Maria is convinced it was excessive cannabis and skunk use in Joanna's early teens that led to her rage and ultimately her murderous rampage. "I don't know what else could have caused such a radical change in her personality from age 14," she says. Maria says that although Joanna had always been strong-minded and hated following rules, it was only after she started mixing with a gang of older drug-smoking boys that she became surly and distant. Chilling: Joanna Dennehy poses with a large serrated knife Before that the two sisters, who shared a room with bunk beds, were so close that they even had a secret language. "She was my big sister and I really looked up to her," Maria says. 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 apologise 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 favourite memories are of the times that she would make up lyrics to songs and teach them to me. There was a big tree in our back garden and we would climb it and sit on branches singing in the evenings after school. Maria, who joined the Army after leaving school and is now an IT engineer in Hertfordshire, recalls that the carefree nature of their childhood came to an abrupt end when Joanna met local boy John Treanor, who at 19 was five years older. She says Joanna became cold and distant. She dropped not only her old neighbourhood friends, but started to see me as a nuisance. I think she was excited by the 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. Their parents, Kevin, 56, who worked in private security, and shop manager Kathleen, 51, toiled long hours for their two children to have a better life. The family's £315,000 four-bedroom home in St Albans, Hertfordshire, was always a pristine showcase. Once a month the girls went to the local library book club then returned home to discuss what they had read with their parents. The girls, Maria says, wanted for nothing and every weekend the family would spend time together, as well as enjoying annual holidays. She always had time for me. We shared all of our secrets Most Sundays we would play football on Redborne Common with dad, or watch cricket. They also took us on walks along old railways tracks. Joanna, the "bright daughter," was their shining light, expected to make the family proud by becoming a lawyer. "Our parents were very protective of us," Maria continues. 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 the early years, Maria says Joanna was quiet, sweet and docile; a real "girlie girl" who loved dressing up and playing with dolls. She never showed aggression. Indeed, she was well behaved and polite compared with her more boisterous younger sister. "Everyone is speculating about why she turned out the way she did," Maria continues. I think the people, the drugs and the environment she went into triggered something dark inside her. It is possible the darkness might never have risen had she not met John, who has since said she was troubled and has painted himself as the victim of her excesses. Maria bridles at this. He spent nearly 14 years with her and had two children. That's a long time to be with someone who you thought was troubled. Differing paths: Maria, who joined the Army after leaving school and is now an IT engineer in Hertfordshire, recalls that the carefree nature of their childhood came to an abrupt end when Joanna met a local boy, who at 19 was five years older Although she refuses to blame him directly for her sister's descent to the margins of society, she believes the start of that relationship was the catalyst for Joanna's demise. She started to skip school and openly defied mum and dad when they banned her from seeing John. Joanna used to sneak him into the house and she wrote about him in her diary. I showed it to them. I wasn't being mean. I just wanted my sister back. After Kevin confronted John, reminding him that Joanna was under age, the pair ran off together. They were later found living in a tent in scrubland at the back of the family's garden. When her parents threatened to move from the area, Joanna said she would only go if her boyfriend could live with them. Mum and dad were beside themselves. They started to chaperone her everywhere and grounded her, but John would wait outside the house or near her school," Maria says. The people, the drugs triggered something dark inside her Joanna continued to truant and her grades plummeted. One afternoon, her parents were brought into the school after she turned up drunk and burnt her school books. They were devastated and grounded her. But despite their best efforts, she continued to rebel. Maria watched helplessly as her parents suffered. They tried to shield me from the worst of it. Sometimes they said Joanna was staying with our nan or visiting friends. Perhaps they were afraid I might be influenced, but I saw mum crying all the time. No one seemed able to reach the increasingly out-of-control Joanna. She ran away from home frequently. Eventually, even the police grew tired of the yo-yo search and return. Just before her 16th birthday they refused to intervene. She never returned to live under her parents" roof again. "Mum and dad were devastated," says Maria. Occasionally she would get in touch with them, but only for money. Studies have shown teenagers who regularly smoke cannabis are in much greater danger of developing schizophrenia and psychosis. In court, it was argued that Joanna, now detained under the mental health act, showed signs of a psychopathic disorder. Cutting ties: Neither Maria, who has a seven-month-old daughter, Jasmine, nor her parents have been to see Joanna (pictured) since she was arrested When she got pregnant at 16 she called her parents and said she wanted to come home. They went to meet her in Milton Keynes and were appalled by her state. Her head was shaven and she was clearly stoned. They tried to bring her back, but it was just another ruse to get money. She said they would only see the baby if they paid her. They didn't. Joanna and John had two daughters in quick succession and no one knew where they were living. At 15, after leaving school, Maria decided to join the Army. By 21, as her sister was living a squalid life of booze and drugs, Maria was on tour in Helmand province as a radio operator on patrol. She faced "many terrible situations" which are too painful to talk about. During a harrowing six-and-a-half-month tour she returned to camp from a particularly grim patrol and resigned, returning home a year later. She would find her way back to Afghanistan three years later as a civilian contractor for Nato. She also did a stint with the Foreign Office. But she never forgot her sister, whose name still brought tears to her mother's eyes and a sad look from her father. "I began searching for her while I was in Afghanistan," she says. I wanted to see if she was all right and if there was a way back for us as a family. In 2009, Maria was on leave when she found John's name on the electoral roll in Cambridge and drove to the address on a rundown council estate. When an old woman opened the door I said sorry and turned to walk back to my car, thinking I had the wrong address. But then a weary voice called my name. I saw it was indeed Joanna. She looked so old and rough, that I barely recognised her. Her face was drawn and haggard, her hair unwashed. There was a tattoo on her cheek and she did not look anything like the sister I remembered. The inside of the house was a hovel. It was so dirty that I refused her invitation to sit down. She did not look anything like the sister I remembered Joanna said she was sick of her lifestyle and wanted to make things better for her two young daughters, who Maria met for the first time. But when Maria phoned the house later that night, John told her Joanna had packed up and left. "I was gutted because I had hoped we were about to turn a corner, but she lies all the time and is very good at it," says Maria. I called her mobile and she became abusive before cutting me off. It was the last time that we spoke. Neither Maria, who has a seven-month-old daughter, Jasmine, nor her parents have been to see Joanna since she was arrested. When asked why, her eyes widen. Why would we? She washed her hands of us a long time ago. We don't talk about her, except on her birthday or when my mother recalls something nice about her from our childhood. John is now married and lives with his wife and the two children in Manchester. He refuses to get drawn in a "slanging match" with Joanna's family, but will only say: "You can write what you want about me. All I care about is that my children are safe. Maria says the past year has been bittersweet. Now that I'm a mother I can appreciate just how much my parents are going through. They did their best, but no amount of love from us could save Joanna.