The jury in the case of a man accused of murdering Borehamwood teenager Catherine Wynter are expected to consider their verdict on Monday after Judge Andrew Bright QC has finished his summing up of the case.
Tony Bushby, 19, who was said to be Katy's secret boyfriend is accused to stabbing her to death while she babysat her nephew and niece at a house in Beech Drive, Borehamwood on Boxing Day night.
The prosecution at St Albans crown court allege Bushby had created four fictional Facebook friends to convince naive church-goer Katy to trust him and like him.
The jury has heard that when her mother, Joy Davis, called on the morning of December 27 to check on them the children ran down the stairs of the house saying: "Grandma, Grandma Katy's dead."
The 19-year-old art student died from a severe wound to the neck that penetrated both her jugular veins and a stab wound to the stomach that penetrated her vital organs. There were 13 significant stab wounds, said pathologist Dr Nat Carey.
Katy, who met Bushby at West Herts College in Watford, was shy and secretive about their relationship and rarely discussed it, according to a friend.
When asked to explain why Katy's blood was found on his own front door Bushby said he had been given a pair of bloodied gloves by a man called Dan Tress because he was concerned because his hands were cold. The prosecution say Tress does not exist and is a fictional Facebook friend created by Bush by.
Bushby of Digswell Close, Borehamwood denies murder.
He told the jury: "I didn't kill her. I honestly didn't kill her. If there was one person in the world who didn't deserve that it was her."