Elizabeth Edwards, 49, and her daughter Katie, 13, were found dead at Dawson Avenue in Spalding in April
A 15-year-old girl has been found guilty of murdering a mother and daughter.
The teenager, who cannot be named, was 14 when she and her boyfriend stabbed Elizabeth Edwards, 49, and her daughter, Katie, 13, as they slept at their home in Spalding, Lincolnshire.
The girl had denied murdering the two women but admitted manslaughter on the grounds of diminished responsibility.
A 15-year-old boy admitted murder at the start of the trial.
Both teenagers will be sentenced at a later date.
A jury of seven men and five women at Nottingham Crown Court took just two and a half hours to reach their verdicts.
During a six-day trial the court heard how the teenagers meticulously planned the murders before carrying them out.
The bodies of Mrs Edwards and her daughter were found on 15 April at their home.
Mrs Edwards was stabbed by the boy eight times, twice in the throat. One blow injured her jugular and the other almost completely severed her windpipe.
He then checked her pulse to make sure she was dead.
Katie Edwards was stabbed twice in the neck with severe force before she was smothered by the boy.
The girl, who did not physically take part in the killings told police she heard Mrs Edwards “struggling and gurgling” and said she heard Katie Edwards say “I can’t breathe” as she was smothered with a pillow.
Following the killings the couple took a bath and watched four Twilight movies before they were arrested.
The court heard the teenagers had planned to commit suicide after the killings.
The knife used to kill both women – a black-handled kitchen knife with a 20cm blade – was found discarded in Katie’s bedroom.
Prosecutor Peter Joyce QC described the murders as “cold, calculated and callous”.
In her police interview the girl told officers she had “felt like murdering for quite a while”.
She told detectives she and her boyfriend formed their plan to kill the two women on April 9, four days before the killings.
She said: “[He] jokingly said ‘I really want to kill [Mrs Edwards]’ and I said ‘So do I’. He recognised the look in my face that I was not joking and then he said ‘Are you serious?’ and I said ‘Yes’. Then I said ‘Are you?’ and he said ‘Yes’. So we planned what would happen.”
She said that following the killings she “felt fine”.
“I was OK with it. Just the fact that it happened so quickly gave me peace of mind.”