Josie, then nine, her mother, Lin, and sister, Megan, were attacked as they walked along a country lane in Chillenden, near Canterbury, Kent, on 9 July 1996.
All three were tied up and then repeatedly battered with a hammer in a 15-minute attack.
The family's pet dog Lucy was also killed.
Michael Stone, 38, of Gillingham, Kent, denies murdering Dr Russell, 45, and Megan and the attempted murder of Josie, now 11.
Dr Russell was battered more than 15 times and suffered such severe head injuries that her brain was almost severed at its root, Maidstone Crown Court was told. Megan's skull was split from side to side and Josie will always remain impaired as a consequence of her injuries, Ann Rafferty QC, for the prosecution, told the jury of eight women and four men.
The girls had attended a swimming gala in Canterbury earlier that day and the three had been walking from Goodnestone primary school along Cherry Garden Lane to their cottage in Chillenden at about 4.30pm when they were confronted by their attacker.
Although no scientific evidence links Mr Stone to the crime, Ms Rafferty said his confessions to inmates while on remand would be evidence against him.
The trial continues.
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