Two 14-year-olds carried out the "cold, calculated and callous killings" of a mum and her 13-year-old daughter before calmly watching an episode of Twilight, a court has heard.
The boy and girl, who cannot be named for legal reasons, planned the killings for several days after meeting at a McDonald's to discuss their intentions, a jury at Nottingham Crown Court was told.
The bodies of school dinnerlady Elizabeth Edwards, 49, known as Liz, and her daughter Katie, 13, were found at their semi-detached home in Dawson Ave, Spalding, Lincolnshire, on April 15 this year.
Police later arrested a 14-year-old boy and a 14-year-old girl in connection with the deaths.
The girl, now 15, denies two charges of murder. The jury heard a 15-year-old boy has already pleaded guilty to murdering the mother and daughter.
Peter Joyce QC, prosecuting, told them: "The killings happened within moments of each other. The mother was killed first. She was killed while Katie slept in a nearby bedroom.
"They were both stabbed through the throat in their beds at their home."
The jury heard the boy carried out the murders but the girl's defence to murder is that her responsibility for the killings was diminished by her mental state.
But Joyce said the girl was as guilty of murder as the boy.
Joyce said the prosecution case is that the girl, together with the boy, "planned and carried out cold, calculated and callous killings" of Liz and Katie Edwards.
The killings came to light when three police officers forced entry through the front living room window of the pair's home. Officers went upstairs to find the two bodies.
Police visited the house at 9.46pm on the Thursday, but got no response. A police officer heard a dog barking when he returned at 9.30am on Friday.
Joyce said the girl "held a grudge" against Liz Edwards and agreed with the boy to kill her and her daughter Katie.
"They were serious in their intention. They meant it to happen. On the Tuesday they met at McDonald's and further discussed their plan."
Joyce said that the boy took four knives to the house in his backpack. Originally the plan was that the boy would kill Liz Edwards and the girl would kill 13-year-old Katie but the boy carried out both killings.
He stabbed Liz Edwards in the throat as he pinned her down while kneeling astride her.
"The girl was able to hear Liz Edwards struggling and gurgling while the killing took place. She went into the bedroom and saw the boy with a pillow over Liz Edward's head. There were blood splatters on the wall and also blood in the floor and blood on the bed. The boy checked that Mrs Edwards was dead by checking her pulse."
Joyce said the boy then went into Katie Edwards's bedroom and stabbed her.
"It seems probable that Katie was also smothered with a pillow and from the position of her body may have tried to move away from her attacker.
"After the killings the girl helped the boy take off his clothes and they took a bath together to wash off any blood."
He added: "Afterwards they watched a couple of episodes of Twilight."
Joyce said a post-mortem examination revealed Liz Edwards had been stabbed twice in the neck cutting her jugular vein. She was also stabbed in the right shoulder and had cuts on her hands, which may have been inflicted as she attempted to fight off her attacker.
Katie Edwards died from a haemorrhage to the neck and smothering.
Joyce said: "The prosecution case is that the girl is as guilty of murder as the boy. She, together with him, planned and carried out the cold, calculated and callous killings. She has shown no hint of remorse."
The trial continues.