Armed police are protecting the judge and several lawyers involved in prosecuting the property tycoon Nicholas van Hoogstraten for manslaughter.
Some of the witnesses who gave evidence against the man once described by a judge as an "emissary of Beelzebub" have also been offered protection by Scotland Yard.
Mr van Hoogstraten was freed last week after his conviction for hiring two gunmen to kill a rival was quashed. He had served 12 months of a 10-year sentence.
Protective officers have been deployed amid concerns that associates of the multimillionaire will seek revenge on those involved in the manslaughter case and a subsequent multimillion-pound com- pensation claim against him.
A police source described associates of Mr van Hoogstraten as some of the most "vindictive and evil" people that the Metropolitan Police had encountered.
Among those being guarded by the Met's Criminal Justice Protection Unit is the original trial judge, Mr Justice Newman. He is understood to be guarded by armed officers when in a vulnerable or public location.
Panic buttons, alarms and police hotlines are thought to have been fitted at the judge's home, and those of several of the prosecuting lawyers and witnesses. The protection unit is part of the Met's Specialist Crime Directorate, based at Scotland Yard.
Seventeen months ago at the Old Bailey, Mr van Hoogstraten, 58, was cleared of murder but convicted of the man- slaughter of Mohammed Raja, 62, a rival landlord. Robert Knapp, 56, and David Croke, 60 - the men who shot Mr Raja at his home in south-west London - were sentenced to life.
During the trial, the Crown's two most important witnesses, including a former girlfriend of Mr van Hoogstraten, failed to give evidence. One witness, Michaal Hamdam, a Lebanese businessman, fled the country after an attempt was allegedly made to kidnap his girlfriend's daughter from school.
The Attorney General has asked police to investigate claims of witnesses being intimidated into changing or retracting evidence.
The multimillionaire has gained a reputation for ruthlessness and viciousness. During a trial in 1968 he was given a four-year sentence for damaging the home of a clergyman with a hand-grenade - the most serious of nine convictions.
In a court appearance in 1992 he said the trial judge was due "a come-uppance", adding: "I'll get him."
On his release from jail last week, the man who once described his politics as "to the right of Attila the Hun" vowed to sue almost everyone involved in his conviction.
Mr van Hoogstraten is taking legal action against the family of Mr Raja, who have sued Mr van Hoogstraten over an alleged property fraud and had his finances frozen. This case is subject to an appeal. The tycoon, who owns a mansion in East Sussex, has described his tenants as filth, business rivals as maggots, and ramblers as scum and perverts.
- More about: