It was hoped that Josephine Russell, nine, would provide clues to the deaths of her mother Lin Russell, 45, and her sister Megan, six.
Their bodies were found early yesterday in a wooded area near Chillenden, about 10 miles from Canterbury, Kent. The family's pet terrier lay dead nearby. Josephine, who has life-threatening head injuries, is at an unnamed London hospital.
Mrs Russell had left the family home in the village of Nonington to pick up her children from school in nearby Goodnestone at around 4pm on Tuesday. She and her two daughters were seen leaving the school. It is thought that Mrs Russell collected the girls up from a school swimming gala, but failed to take them to Brownies.
Mrs Russell's husband, Shaun, a researcher at the University of Kent at Canterbury, set off to search the route his wife would have taken. When he found nothing, he called the police.
The bodies were found near a wooded track next to farmland on the route home. It is thought that they were in undergrowth 10 yards from the path.
The case has echoes of the unsolved murder of Rachel Nickell, 23, who was knifed to death in front of her son Alex, two, on Wimbledon Common in 1992. Kent police stressed, however, that they were not yet linking the investigation with any other inquiry.
They said that they would have to await the outcome of post-mortem examinations being carried out last nightbefore they would be sure how Mrs Russell and her daughter died.
Earlier in the day, a police spokeswoman said that Josephine could have a key role to play. "Clearly she will be the main witness," she said. Police are hoping to speak to her, though if and when they do so will depend on her condition.
"This girl is probably our greatest hope of finding out what happened," the spokeswoman added.
Dr Russell arrived in the village around last July, having moved from Wales to take up a position as a post-doctoral researcher. Mrs Russell and their daughters joined him in the autumn.The family were Welsh-speaking but both Megan and Josephine spoke English. A neighbour said: "They were very happy little girls - delightful."Reuse content