Spalding murders: Teenage girl and boyfriend become youngest couple ever convicted of murder in Britain

After the killings the couple took a bath and watched four Twilight movies

A 15-year-old girl has been found guilty of murdering a mother and daughter in Spalding, Lincolnshire.

The teenager, who was 14 years old at the time, cannot be named. She was found guilty after her 15-year-old boyfriend admitted killing the two women at the beginning of the trial.

The pair are the youngest couple ever convicted of murder in Britain.

Elizabeth Edwards, who was 49 years old, and her 13-year-old daugher Katie were stabbed in the neck as they slept at home in April.

The prosecution had alleged during the trial that although the girl did not physically take part in the killings, she was “as guilty of murder” as the boy was.

A jury of seven men and five women at Nottingham Crown Court took just two hours and thirty minutes to reach the verdicts.

Prosecution argued that although the girl did not physically take part in the killings, she was 'as guilty' as the boy was (PA)

The girl had denied murdering the victims on the grounds of diminished responsibility. A psychiatrist for the defence had said she was suffering from a mental disorder.

But the Crown argued she was not mentally ill at the time of the crime. Forensic psychiatrist Philip Joseph said that the girl was simply in a state of emotional turmoil.

Mr Josph told the court a Bonnie and Clyde-type dynamic motivated the teenagers to carry out the killings.

(PA (PA)

Ms Edwards was stabbed eight times by the boy, including twice in the neck. One of the cuts almost completely severed her windpipe. He then checked for a pulse to see if she was dead.

The 15-year-old girl said she could hear the Ms Edwards "struggling and gurgling" as she was attacked.

Katie was stabbed twice in the throat before she was smothered.

After the killings the couple took a bath, had sex and watched four Twilight films, although the court heard that the pair had planned to take their own lives.

The girl told officers during a police interview she had "felt like murdering for quite a while" and said "it just sort of happened".

She also said she and her boyfriend had planned the killings four days before and that following the murders she "felt fine".

Both teenagers face indefinite detention at Her Majesty's pleasure – the juvenile equivalent of an adult life term. They will be sentenced at a later date.