Stewart heard her husband struggling as Howell tried to kill him

During police interviews, Stewart said she heard a struggle in the bedroom where her husband was sleeping, after Howell had gone in with a hose pipe to poison him.

She said she looked out into the hallway and saw her husband lying in his boxer shorts.

“I didn’t want to hear it, I put my hands over my ears, I didn’t want to hear it, I was so scared,” she told police.

The prosecution told the jury during the first day of evidence at Coleraine Crown Court about interviews given by Stewart when she was arrested in January 2009.

At first she told police that she did not know what Howell was planning to do.

“It was his plan,” she told detectives. “I didn’t want to know.”

But the court heard that in later interviews that Stewart had told police she had encouraged her husband to take a temazepam tablet before Howell arrived to kill him.

“Colin gave me the tablets to give to him,” Stewart said.

“If he hadn’t taken it I would have had to give him something ... he had to have something in him to relax a bit. If Trevor hadn’t taken it he (Howell) couldn’t have gone on with it.”

The jury were also told that during interviews, Stewart admitted leaving the garage door of the her house open to let Howell drive in with his dead wife in the boot of the car.

The interviews also revealed details about her relationship with Howell, who is currently serving a 21 year sentence.

Stewart described Howell as ‘very controlling’, and she said he had a “psychological” hold on her.

Interviews also revealed that Howell took her to England to have an abortion.

Prosecuting barrister Ciaran Murphy QC told the court that there was no doubt Stewart had engaged in a joint enterprise to kill Mrs Howell and Mr Buchanan.

“The purpose was to rid them of their partners so they could be together,” he said.

Mr Murphy added: “She stood feet away knowing her husband was struggling for his last breaths. She showed total and utter callous disregard for her husband and endorsed and encouraged exactly what Colin Howell was doing.”

The trial continues and is expected to last for four weeks.