Coleraine woman Hazel Stewart, convicted of murdering her husband and her former lover's wife, has been sentenced to a minimum of 18 years in prison at Belfast Crown Court.
The 48-year-old was jailed for life earlier this month after being found guilty of killing Trevor Buchanan and Leslie Howell in May 1991.
Her former lover and co-accused, dentist Colin Howell, 52, is already serving a 21-year term after he confessed to committing the double murder in May 1991.
Howell first gassed his wife and then Constable Buchanan as they slept at their homes in Coleraine before stage managing the deaths to make them look like they killed themselves in a suicide pact.
The bodies were found in a car filled with poisonous carbon monoxide fumes in a garage behind a row of houses known as the Twelve Apostles in the seaside town of Castlerock, Co Derry.
Police reopened the investigation in January 2009 when Howell, a father-of-ten, admitted he murdered them. Stewart, who later married former police Chief Superintendent David Stewart, was arrested hours later.
She first claimed she wanted no part of Howell's plan to murder, but eventually confessed her role in the deaths before agreeing to concoct a cover-up story which fooled investigating detectives 20 years ago.
A jury unanimously found her guilty at the end of a 15-day trial.
Mr Justice Anthony Hart accepted Stewart had played a secondary role to Colin Howell.
'Nevertheless, her responsibility for what happened was very substantial, and the minimum term must reflect that,' he said.
Mr Hart noted that Howell had received credit for pleading guilty - he would have received 28 years if he had not - and stressed that the crimes would never have been uncovered if the dentist had not confessed.
'Hazel Stewart cannot claim any such reduction in the minimum term to be imposed in her case because she pleaded not guilty.'
Mr Hart said she had shown little real remorse and ordered that she serve at least eighteen years in jaill before being considered for release on parole.
Among those in the packed public gallery of the court were Hazel Stewart's husband, son and daughter, and relatives of the two victims of the murder plot.
