THE father of murdered schoolgirl Katie Edwards has bought the plot beside her grave, saying in an emotional post that he "cannot wait to lay in it when the time comes".

Edinburgh-born dinner lady Elizabeth Edwards, 49, and 13-year-old Katie Edwards were murdered in April this year in a "senseless and unprovoked" double attack.

A 15-year-old girl, who cannot be named for legal reasons, was found guilty of murdering the pair, despite claiming diminished responsibility.

Her boyfriend, also now 15, pleaded guilty to murder before the trial began. They are believed to be the youngest defendants to be convicted of double murder in a British court.

The murdered mother and daughter were recently buried, but in separate ceremonies and in graves that were not beside each other.

Mr Edwards, Katie's father and estranged partner of Ms Edwards, confirmed that he had bought the adjacent plot to his daughter, saying on Facebook: "It's in black & white now kido [sic]. Just time now just time."

On another post, Mr Edwards, who is also father to Katie's older sisters, said: "Got to say now I own the spot I can not wait to lay in it when the time comes no sooner so I have to stress that."

The 43-year-old also wrote: "One day I will lay by your side to hold your hand or may be your hold mine to Guide my soul. I know in time my bones will lay next to yours ... painful as life is, one day you and I will be at peace laying together as daughter and father."

Elizabeth and her daughter Katie lived together in Spalding, Lincolnshire, when they were murdered by a 14-year-old boy and his girlfriend, also 14, who had forced their way into the pair's home.

Post-mortem examinations found signs of defensive injuries on the older victim's hands, suggesting she had tried to fight off the boy, while her daughter had been stabbed twice in the neck.

The girl admitted manslaughter but denied murder, claiming to be suffering an abnormality of mental function which impaired her ability to form rational judgments.

However at a five-day trial at Nottingham Crown Court the jury heard that the girl was not suffering from a mental illness when she and her boyfriend planned the killings "to the letter".

The jurors heard how the defendants' toxic Bonnie and Clyde-style relationship "led on to" the killings, and took just two-and-a-half hours to convict her of murder.

Her boyfriend, who stabbed and smothered the victims as they slept, pleaded guilty to murder before the trial began.

During the trial, the jury also learned that Katie would have celebrated her 14th birthday, with her father posting on Facebook at the time: "Just a simple I love you Katie Edwards forever young happy birthday love DAD xx"

In lengthy admissions to police, the schoolgirl said she and her boyfriend had planned the killings after a conversation which began with a joke suggestion of committing a murder.

Consultant forensic psychiatrist Dr Philip Joseph told the trial he believed the couple's "intense, toxic" relationship was the primary reason for 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."

In an interview with the Sun on Sunday, a friend of the girl is believed to have said that she was once "funny, happy-go-lucky and loved jokes".

However she had changed when she met her boyfriend, who was supposedly controlling, which made her increasingly distant.

Both killers will be sentenced next month.