A teenage girl convicted of a double murder with her boyfriend, admitted plotting the killings in a chillingly matter of fact police interview, it can now be revealed.

The girl, who was 14 at the time of the brutal murders, was described as being the "driver" behind the plot to kill dinner lady, Elizabeth Edwards, 49, and her 13-year-old daughter Katie in Spalding in April.

After persuading her 14-year-old boyfriend to take part she planned the "cold and calculated" attack, telling police: "I've felt like murdering for quite a while and [the boy] just hates me being upset. It just sort of happened."

After carrying out the murders the couple took a bath, had sex and settled down to watch the teen vampire film, Twilight.

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The pair are thought to be the youngest couple convicted of a double murder in Britain.

During her police interview she described how the boy had produced a bag containing four knives and had said to her: "Are you ready to do this?" to which she replied that she was.

The boy then attacked Elizabeth Edwards as she slept, pinning her to her bed before repeatedly knifing her in throat and voicebox to prevent her from crying out.

Liz Edwards, left, pictured with her eldest daughter Mary, was killed in her bed. Photo / Facebook
Liz Edwards, left, pictured with her eldest daughter Mary, was killed in her bed. Photo / Facebook

He then attacked her 13-year-old daughter, Katie, before he and the girl took a bath together to wash off the blood.

In her police interview the girl said: "I planned it so we would be clean and refreshed and wouldn't smell of blood. We spent about 20 minutes in the bath.

"I like Twilight, so I said to [the boy] 'Why don't we watch it?' I thought he might like it as well."

Despite the depravity of their actions, the pair, who were likened in court to the infamous American crime due, Bonnie and Clyde, cannot be named because of their young age.

The judge will reconsider whether they should be identified when the pair are sentenced on November 10

The boy admitted the two murders, but the girl was convicted following a five-day trial at Nottingham Crown Court.

While he admitted wielding the fatal stab wounds, the jury heard the girl was the "driver" in the plot, persuading her boyfriend to carry out the killings to satisfy a long-held grudge.

In the months leading up to the killings the girl wrote in her diary, "there is madness in me" and "death is the only way".

The teen killers had a bath after the attack and then watched Twilight, as the girl liked it.
The teen killers had a bath after the attack and then watched Twilight, as the girl liked it.

She was described as a "ticking time bomb" who was fuelled by "sheer contempt and brutality" for her victims.

The court heard that they had talked about taking an overdose together after the murders, but changed their minds and ate icecream and toasted teacakes instead.

They were arrested two days after the murders when police, concerned for the welfare of Elizabeth Edwards forced their way into her semi-detached home and found the bodies of her and her daughter.

Consultant forensic psychiatrist Dr Philip Joseph told the trial that the couple's "intense" and "toxic" relationship had been the primary reason behind the killings.

He told the jury: "A group dynamic can lead you to a course of action you would never have contemplated on your own.

"Bonnie and Clyde...that sort of intense attraction, emotional closeness - them against the world. It's that sort of thing that led on to this."

As the jury returned its verdict the girl sobbed softly and wiped her face with a tissue.

Both killers face indefinite detention at Her Majesty's pleasure - the juvenile equivalent of a life term for an adult.

Detective Chief Inspector Martin Holvey, of East Midlands Major Crime Unit, described the case as having a "shocking impact" on the whole community of Spalding.

He went on: "What makes this case even more shocking is that these two were 14 years of age when they planned and committed these callous, senseless and unprovoked attacks on Elizabeth and Katie.

"This case has left a number of lives in ruins, not only Elizabeth and Katie's family, but also the two juveniles who committed these horrendous crimes."