Paul Bersebach/The Orange County Register/Zuma

Nanette Johnston, the California woman accused of having her ex-NFL lover murder her wealthy, older fiance nearly two decades ago, was found guilty today on charges she plotted her fiance's death for financial gain.

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, inside a wealthy, gated community. 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, now 46, 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, at the time, stood to benefit from a $1 million life insurance policy, $150,000 from McLaughlin's will and access to his beach house.

She was found guilty today of first-degree murder and guilty of the special circumstance of committing murder for financial gain by a nine-woman, three-man jury in an Orange County, Calif. courtroom.

The jury's quick decision in Johnston's case came after heard closing arguments last Thursday.

"The jury only needed about three hours to deliberate and they were very sure about their decision," one of McLaughlin's daughters said after the guilty verdict was read.  "This has been a long time coming and it's closure for us."

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.

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

He was scheduled to be sentenced last Friday but the judge agreed to a request by Naposki's lawyers to delay the sentencing until May.

The defense acknowledged Johnston's affair with Naposki, 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 argued.

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

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

The prosecution said Johnston planned the murder, giving Naposki the key he used to enter McLaughlin's home.

And, they said, Johnston pleaded guilty to stealing half a million dollars from McLaughlin before and after the murder.

"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."

Johnston and Naposki will be sentenced on May 18.  Both face sentences of life in prison without the possibility of parole.

ABC News' Andrea Canning contributed to this report.