Michael Stone was today found guilty for the second time of the murder of Dr Lin Russell and her six-year-old daughter, Megan.
A jury at Nottingham crown court reached the verdict after a second trial was ordered earlier this year when his original conviction was quashed.
It also found him guilty of the attempted murder of Josie Russell, nine years old in 1996 at the time of the attacks.
The judge gave Stone three life sentences.
The four-week trial heard how Josie was found with massive head injuries in a copse in Chillenden, Kent, next to the bodies of her 45-year-old mother, sister and the family dog.
She underwent emergency neurosurgery at King's College hospital, London, but within two months was able to begin communicating to officers what she could remember about the attack.
The court was shown videotaped interviews in which she described a man holding a hammer getting out of his car. He then, according to Josie, demanded money and Lin Russell told her and Megan to run away.
She said the man caught up and hit her on the head before dragging her back to the copse where she remembered trying to prevent the man striking her mother.
Stone was arrested a year after the murders in July 1997, and was unable to give an alibi for when the Russell family were attacked.
While Stone was on remand at Canterbury prison, a fellow inmate, Damian Daley, claimed a man in the neighbouring cell confessed to the Chillenden murders.
Daley, who admitted lying to a previous jury, told the trial the man, said by the prosecution to be Stone, used a heating pipe linking the two cells to talk to him.
The jury of nine men and three women visited the cell during the trial, along with the murder scene.
Mr Justice Poole told Stone that his crimes were horrific.
"Michael Stone, you have been convicted of three terrible crimes," he said.
"There is no need for me to develop that description further."
A gaunt-faced Stone showed little emotion as the foreman of the jury announced the verdicts.
His sister, Barbara, who has fought tirelessly in a bid to clear her brother's name said "not again" as the verdict was read out.
Stone, wearing a cream T-shirt and blue tracksuit bottoms, stared ahead as he was told that he would be heading back to prison.