She was the woman who finally helped police unpick Jeremy Bamber's web of lies and was a key witness in the trial that saw him convicted of the murder of his entire family.
Julie Mugford dramatically changed her statement to officers a month after Bamber slaughter his mother, father, sister and two young nephews at White House Farm.
She told police he had been planning to kill his parents, Nevill and June, for some time and revealed the full details of the chilling phone call he made to her on the night of the murders.
Julie's statement saw Jeremy arrested and charged before his trial the following year.
Her evidence formed a vital part of the prosecution's defence and Bamber was jailed for life.
He is one of the few people in the UK to be serving an entire life sentence.
But in the weeks and days following the murders, Julie seemed to be Jeremy's rock.
She even had to physically support him when he broke down sobbing at the funerals of his parents, sister, Sheila, and young nephews, Daniel and Nicholas.
Bamber had claimed he had been at home on the night of the murders when he received a phone call from his dad saying Sheila was "going beserk" with a rifle.
He was the one who contacted police and appeared to be devastated by the deaths of his family.
Nevill was found dead in the kitchen, while Sheila and June were both dead in his parents' bedroom.
Nicholas and Daniel had been shot dead in their beds as they slept.
Senior detectives in charge of the case believed it was a tragic case of murder/suicide and Bamber was not a suspect.
But then Julie changed her statement and told officers about the depths of Bamber's resentment towards his parents.
She claimed that he had repeatedly said in the months leading up to the murders that he wish he could "get rid of them all".
Julie told police he complained about his "old" father and "mad" mother, who he told his girlfriend were "trying to run his life".
Bamber was also annoyed that his parents were paying for Sheila's flat in Maida Vale, London, and claimed that his sister had nothing to live for while her twin sons were "disturbed".
Chillingly, he had even gone into details about how he would kill his family, mentioning sleeping pills, setting fire to White House Farm and shooting them.
Bamber also said his sister, Sheila, who had serious mental health problems, would make a good scapegoat.
On the night of the massacre, Julie told police Bamber had phoned her to say eh was "p***** off" and that it was "tonight or never".
A few hours later she received a second phone call, where he said: "Everything is going well.
"Something is wrong at the farm. I haven't had any sleep all night ... bye honey and I love you lots."
Bamber then claimed he wasn't the one responsible for the murders but that a friend of the family had carroed out the brutal killings - and that he had paid him.
Police investigated his claims to have paid someone to carry out the murders but the man he had accused had a watertight alibi.
Then, as a direct result of Julie's statement, Bamber was arrested.
Julie's evidence was a key part of his trial and after 18 days he was convicted.
After her testimony had helped convict her boyfriend Julie decided to sell her story abut what life with the killer was really like.
She was paid £25,000 by the News Of The World or her account of what had really happened behind closed doors with Jeremy Bamber.
Julie has now started a new life in Canada.