Property baron Nicholas van Hoogstraten has been held responsible by the High Court for the killing of businessman Mohammed Raja.
Mr van Hoogstraten was cleared of killing Mohammed Raja
The ruling came despite the 60-year-old multi-millionaire, from Uckfield in East Sussex, being cleared of manslaughter in the criminal courts.
Mr Justice Lightman ruled that, on the balance of probability, the businessman was involved in the death.
It is central to a £6m civil action being brought by the dead man's family.
It was claimed in the High Court that Mr van Hoogstraten was a psychopath who arranged for the "assassination".
Mr van Hoogstraten was not present or legally represented during the hearing.
Andrew Mitchell QC, for the Raja family, said in his closing submissions that all the evidence supported one witness's description of Mr van Hoogstraten as "a psychopath".
He claimed that the businessman's treatment of his housing tenants demonstrated his propensity for violence.
Mr Raja, 62, had been in the process of suing Mr van Hoogstraten over a business deal when he was stabbed and shot dead after answering the doorbell at his home in Sutton, south London, in July 1999.
His killers, Robert Knapp and David Croke - who were alleged to have been working for Mr van Hoogstraten - are currently serving life for murder.
Giving judgment following the hearing in London last month, Mr Justice Lightman said he was satisfied "the recruitment of two violent thugs with a shotgun" was for the purpose of murdering Mr Raja.
Mohammed Raja's family continued legal action after he was killed
He said it was more than was needed to frighten or injure him, and the second shot was deliberately aimed at killing him.
The judge said the property tycoon had clearly wanted them to "break" the "thorn in his flesh" and resolve for good his problems with Mr Raja.
"His purpose in murdering Mr Raja has not been achieved because, contrary to his expectations, Mr Raja's family have been as resilient as was Mr Raja in his lifetime in standing up to Mr van Hoogstraten," he said.
In a statement prepared for his defence to the proceedings, Mr van Hoogstraten insisted that, although he had known Knapp for 35 years, he had never employed him in any capacity.
Mr van Hoogstraten was sentenced to 10 years at the Old Bailey in 2002 for the manslaughter of Mr Raja.
However, his conviction was quashed by the Court of Appeal.
The judge ordered Mr van Hoogstraten to pay £500,000 interim costs on an "indemnity" basis within 14 days.
After the hearing, the Raja family said in a statement: "Naturally, we are very pleased with the court's findings, but it has been a devastating and uphill struggle to get here."
Speaking outside the court, Mr Raja's son, Amjad, urged the Crown Prosecution Service to look at the case and see what other action could be taken against Mr van Hoogstraten.
He said the family was determined to finish what his father had started.
"From this judgement today the judge has shown us that at last he has given us justice."