(Paul Bersebach/The Orange County Register/ZUMAPRESS.com)

ABC News' Andrea Canning reports:

The jury heard closing arguments Thursday in the trial of Nanette Johnston, accused of plotting to have her lover kill her far older, millionaire fiance nearly two decades ago so she could collect on an insurance policy and other assets.

"[The prosecutor's] pinnacle evidence of this case, saying my client was involved, is horse manure," Johnston's defense attorney, Deputy Public Defender Mick Hill, said.

"You just listened to two hours of crap in an Irish accent," Deputy District Attorney Matt Murphy said after Hill, who was born and raised in Ireland, finished.

"Anyone who commits murder like this is clever, diabolical, evil," Murphy said, at another point calling Johnston "a con artist and rip off queen."

On Dec. 15, 1994, Bill McLaughlin, a 55-year-old inventor and pharmaceutical mogul, was shot six times by an intruder in his Newport Beach, Calif., home. He was living with Johnston, then an attractive 25-year-old he'd met after he answered her ad in a dating magazine.

No arrests were made at the time, but 15 years later prosecutors re-examined the evidence. They charged Johnston and her lover, Eric Naposki, a former NFL linebacker, with murder. The prosecutor alleged she put Naposki up to the crime so they could make millions off McLaughlin's death. Johnston would benefit from a $1 million life insurance policy, $150,000 from McLaughlin's will and access to his beach house.

The defense said Johnston had a solid alibi and that Naposki acted alone, out of jealousy. Naposki was convicted of first-degree murder last year. He could get life in prison without parole when he is sentenced on Friday.

The defense acknowledged the affair but argued Johnston was an intelligent woman who would never leave her wealthy fiance.

"Hate her as much as you want for being a liar, a cheater  and a thief, but you can't hold her guilty based on that," Hill said.

The prosecution said Johnston planned the whole thing, and gave Naposki the key he used to enter McLaughlin's home. She pleaded guilty to stealing half a million dollars from McLaughlin before and after the murder, they said.

"Bill McLaughlin is worth a thousand times more to her dead than he is alive," said Murphy. "She would become the trustee and has the money. She becomes the golden goose."