The former Special Branch informer, Ken Barrett, has been sentenced to 22 years in jail for the murder of Belfast solicitor Pat Finucane.
Under the terms of the Good Friday Agreement Barrett may be entitled to apply to the Life Sentence Review Body for early release from jail and could be freed within a year.
In passing sentence, Mr Justice Weir said the murder of Pat Finucane was particularly cruel and callous, as it had been carefully planned and mercilessly executed.
He said the object was to attempt to intimidate other members of the legal profession from carrying out their duty.
Earlier, a defence lawyer told Belfast Crown Court there was insufficient evidence that Barrett was the person who discharged the shots which killed Mr Finucane 15 years ago.
Last Monday, Barrett pleaded guilty to 12 charges, including the murder of Mr Finucane and the attempted murder of his wife, Geraldine, at their north Belfast home.
The 41-year-old, who was a member of the Ulster Freedom Fighters - a cover name for the UDA, was one of two gunmen who broke into Mr Finucane's house in February 1989 and shot him in front of his family.
Barrett, from north Belfast, was arrested in London last year and was brought back to the North. He has been held in an isolated cell at the top security Maghaberry Prison near Lisburn in Co Antrim.
Barrett's guilty plea has increased pressure on the British government to hold an independent public inquiry into allegations of security force collusion in the killing.
Mrs Finucane has repeated her call for an inquiry which the government put on hold until after the Barrett trial.
