A mother and daughter were stabbed to death in their beds by two teenagers in a “cold, calculated and callous” killing, a court has heard.
Elizabeth Edwards, 49, and her 13-year-old daughter Katie were found dead at their Lincolnshire home in April.
A jury has been told the pair, of Dawson Avenue, Spalding, were murdered by a boy and girl aged 14 at the time.
At Nottingham Crown Court the boy, now 15, pleaded guilty to their murders. The girl, also 15, denies murder.
However she has admitted killing them, but has claimed diminished responsibility, the prosecution said.
Neither of the teenagers can be named because of their ages.
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Opening the case, prosecutor Peter Joyce QC said the victims had been stabbed in the throat by the teenage boy after he and the girl had plotted to kill them.
He said: “There is no doubt that [the girl] was as responsible for the killings as [the boy] since she has pleaded guilty to manslaughter, but she is saying as her defence to murder that her responsibility for the killings was lessened or diminished by her mental state.
“She is not denying that she was just as involved as [the boy] in being party to the killings, she wanted the killings to happen; [but] she is asserting that her mental condition at the time reduces her responsibility from murder to manslaughter.
“The prosecution case is quite simple; she will not succeed in proving that her responsibility was diminished and it is our case that she is as guilty of murder as was [the boy].”
The court heard the killings took place on the night of 13 April.
Mr Joyce said that the boy stabbed Mrs Edwards eight times, including three times in the throat, injuring her jugular vein and almost completely cutting through her windpipe.
He said the boy had then stabbed Katie twice in the neck before smothering her with a pillow.
He said the two teenagers had planned to stab their victims in the throat so they “would not make a noise”.
The court heard that after the killings the two teenagers took a bath together before later watching Twilight films.
The victims’ bodies were discovered by police on 15 April, four days after the accused began plotting their deaths.
Mr Joyce said it had originally been intended the boy would kill Mrs Edwards and the girl would kill Katie Edwards.
Jurors were told the knife used to stab both victims was discovered on a table in Katie’s bedroom.
In her police interview the girl told detectives the plan had been for her and the boy to take their own lives after the killings.
Mr Joyce said: “The prosecution case is that this girl together with the boy planned and carried out the cold, calculated and callous killings.
“Afterwards there has not been a hint of remorse and the prosecution case is that she is as guilty as the boy of the murders.”