“You were in a hermetically sealed world of your own of deep, deep selfishness and immaturity where only your feelings mattered and nobody else’s.
“There was remarkable pre-meditation and planning. The precise mechanism was planned and pre-planned several times. It was on any view substantial and meticulous.
“The fact that both defendants expressed happiness at what they had done is an aggravating feature.
“This was an entirely joint offence. You were in it together from the beginning. You conceived of the killings together, you planned it together, replanned it together and carried it out together step by step.”
During the trial the jury heard that Liz and Katie Edwards were the victims of “cold, calculated and callous killings” after being attacked as they slept in their home at Dawson Avenue, Spalding.
Peter Joyce QC, prosecuting, said that they each planned to kill one victim but the girl changed her mind at the last minute.
Instead the boy stabbed both victims in the throat admitting afterwards that the plan was to aim for the voice box so neither would scream.
Mrs Edwards (49) was stabbed twice in the neck with the force sufficient to cut almost completely sever her windpipe. Her jugular vein was cut and she died a short time later. She had suffered five knife wounds to her hands as she tried desperately to protect herself.
Katie (13) had two stab wounds to the neck one of which cut a main artery. Her body was found with a pillow over her head and her death was due to a combination of blood loss and smothering.
The bodies were found after police broke into Mrs Edwards‘ home in Dawson Avenue, Spalding.
The teen killers then watched an episode of the vampire-themed fantasy Twilight before having sex together. The jury heard the pair were in a “toxic relationship” and a “ticking time bomb waiting to go off”.
The girl later told a psychiatrist that they had planned the murders and in the days leading up to the killings she sat at her school desk excited at the prospect of what they were going to do.
The girl admitted two charges of manslaughter by reason of diminished responsibility between April 12 and 15, 2016, but denied murder. The jury took just two and a half hours to convict her of murder at the end of a six-day trial. The boy admitted two charges of murder. Neither can be identified as a result of a court order. Both were 14 at the time but are now 15.
