A jury was urged to avoid a miscarriage of justice today as the murder trial of Hazel Stewart in the North drew to a close.
A barrister for the accused, 48 today, said her dentist lover, Colin Howell, was responsible for the murders of his wife and Stewart's first husband and impossible to stop, but there was no plan or joint enterprise.
Paul Ramsey addressed Coleraine Crown Court on the 14th day of her murder trial.
"This is a difficult, distressing and heart-rending case. We have listened day after day to horrific, almost unbelievable evidence as to what happened on that night in 1991," he said.
"It is a tragedy - but we must not compound that tragedy by a miscarriage of justice.
"I would ask you to consider the evidence in this case should give you cause to hesitate, to pause and to resist the headlong urge to convict that the Crown have urged upon you."
Prosecutors have insisted the killings of their spouses were a joint enterprise, a plan executed by dentist Colin Howell and Stewart to rid themselves of their respective partners for them to be together.
Stewart, from Ballystrone Road, Macosquin, Coleraine, who has denied the two murders, sat impassively in the dock today.
Her husband, Pc Trevor Buchanan (aged 32) and Lesley Howell (aged 31), the wife of her lover, were found dead in a car filled with carbon monoxide fumes in a garage behind a row of houses known as the Twelve Apostles in the seaside town of Castlerock, Co Derry, in May 1991.
At first police thought they had died in some sort of suicide pact because of the distress over their spouses' affair.
It was only when Howell (aged 51), first confessed to his church elders and then police in January 2009 that he had murdered them that Stewart was arrested by investigating detectives.
Howell, a father of 10 from Glebe Road, Castlerock, is serving a 21-year jail sentence after pleading guilty to the murders.
He first gassed his wife as she slept on the sofa of their home in Coleraine.
He then drove her body to the far side of the town, where he murdered Pc Buchanan by the same method before taking the two bodies away to stage-manage the suicide.
Mr Ramsey acknowledged that Stewart had failings, was flawed, but it was not her fault the prosecution had not charged her with what she had done, which was assisting an offender and withholding information.
But he told the jury: "When you sift carefully and slowly through the evidence you will slowly, inexorably arrive at the only conclusion that you can come to in this case. That there was no plan, this was never a joint enterprise, these were crimes carried out by this ruthless man who had passed the point of no return.
"She had no part to play in the murder of Lesley Howell.
"We ask you members of the jury to return the right verdict, the proper verdict, the just verdict and the only verdict. We ask you to find Hazel Stewart not guilty."
According to the prosecution, Stewart took actions, including making sure no car was in the garage when Howell pulled up at the house with his wife's body in the boot, ensuring her husband was drugged asleep, setting out clothes to dress his body in, and afterwards changing the sheets on which Mr Buchanan had struggled for life, and burning the rubber hose used to carry in the noxious fumes.
But Mr Ramsey said they were the actions of a woman caught unawares by the event.
She did not even have a Stanley knife to cut up the hose, there was an object in the garage which Howell reversed over when he drove into her garage to kill Mr Buchanan, and he was concerned the noise might wake up Mr Buchanan.