A 15-year-old boy has admitted to the murders of a mother and her daughter.
The bodies of 49-year-old dinner lady Elizabeth Edwards and her 13-year-old daughter Katie were found at a property in Dawson Avenue, Spalding, Lincolnshire in April.
A 15-year-old girl is also on trial at Nottingham Crown Court, she admits manslaughter but denies murdering the woman and her daughter.
The teenagers who cannot be named for legal reasons were both 14 at the time of the killings.
Opening the case for the prosecution, Peter Joyce QC said of the victims: "They were both stabbed through the throat in their beds at their home."
Both teenagers are alleged to have planned the killings before carrying them out at the house in Spalding, Lincolnshire on April 15.
The bodies were found by police who broke down the door to the address on April 15, about 36 hours after the murders.
Both teenagers were arrested shortly after officers made the grim discovery.
Mr Joyce told the jury: "Let me make it plain from the very outset, what it is you're trying and what you're not.
"She (the defendant) is not denying that she was just as involved in being a party to the killings.
"She wanted them to happen."
He added: "She is asserting that her mental condition at the time reduces her responsibility from murder to manslaughter."
The Crown's QC said: "The prosecution's case is that she will not succeed in proving that her responsiblity was diminished."
He added that the defendant had "shown no hint of remorse" since the killings.