Colin Howell tried to convince Hazel Stewart to go along with his murder plan by telling his lover her abortion proved she could kill, the court heard today.
The mother of two alleged the killer dentist used the depraved logic when he outlined his plot to kill his wife Lesley and her policeman husband Trevor Buchanan.
She told investigating officers: "He threw up my abortion - he said sure you've killed a child, what's the difference of killing other people."
The claim was heard by the jury at Coleraine Crown Court as interviews Stewart gave to police in the wake of her arrest in January 2009 were played.
Howell arranged for Stewart to have the secret abortion months before he killed their respective spouses in May 1991.
Throughout the police questioning, Stewart insisted the murders were Howell's idea and she had not agreed to it.
She said the dentist was a "psycho type" and she feared for herself and her young children Andrew and Lisa if she did not co-operate when he arrived at their house with the body of his wife in the car.
"I was crying, I was saying 'no, this is not going to happen, you are not doing this', but he was adamant he had started something and he was going to finish it.
Detective Geoff Ferris asked why she had not tried to stop him.
"What could I have done," she responded.
"If I had screamed or whatever the children would have woke, maybe he would have attacked them, maybe he would have attacked me. I don't know, I don't know."
But she acknowledged that she should have intervened.
"I should have ran down to the room," she said.
"I should have stopped it."
She added: "I have to live with that."
Mr Ferris claimed if Stewart was really opposed to the murder she could have done something to ensure it would not have happened.
"It shouldn't have been allowed to happen if you're saying it happened against your will; it shouldn't have happened," he said.
The officer then challenged her why she had not done something when Howell first mentioned his intentions with her during a meeting prior to the murder.
"I should have told somebody," she conceded.
"I should have gone to the police."
"I should have told Trevor."
Again Stewart claimed she did not take action because Howell controlled her and she was in fear.
Mr Ferris pressed her to explain what she meant by fear and asked if the dentist ever hit her.
She said he had not, but claimed he manipulated her and she was scared about what he could do.