Paul Bersebach/The Orange County Register/ZUMAPRESS.com

ABC News' Andrea Canning reports:

Jury selection is under way in the trial of Nanette Johnston, who is accused of plotting to have her lover kill her far older, millionaire fiancé so she could collect on an insurance policy and other assets nearly two decades ago.

Nanette Johnston, 25, was the live-in girlfriend of inventor William McLaughlin, 55, of Newport Beach, in a wealthy, gated community in California.

Johnston, a beautiful woman with two young children, met McLaughlin after he responded to an ad she placed in a dating magazine for wealthy men. Billing herself as a classy and "well-educated woman who knows how to take care of her man," she caught his attention. They developed a relationship and she moved in with him.

The pharmaceutical mogul was killed on the night of Dec. 15, 1993, by an intruder who shot him six times in the chest inside his home.

At the time, Johnston was away from the house at her son's soccer game, but prosecutors believe she gave her lover - former NFL linebacker Eric Naproski -  a key to the house so he could enter and commit the killing, according to a report in the Orange County Register.

Police weren't able to bring a case because they lacked evidence, but they reopened the investigation in 2009, re-interviewing witnesses and re-examining evidence. They then charged Johnston, now 46, with putting Naproski up to the killing.

She has denied the allegations, and her attorney said she would never have left her wealthy fiancé, adding that Naproski acted alone out of jealousy.

But prosecutors say Johnston had everything to gain, including a $1 million life insurance policy, $150,000 from McLaughlin's will and access to his beach house.

The woman had already been in trouble with the law before regarding McLaughlin's finances. According to ABC News affiliate KABC TV in Los Angeles, Johnston - who is also known as Nanette Packard - was charged with grand theft in 1995 for allegedly stealing about $500,000 from McLaughlin's account before and after his murder. She pleaded guilty and was sentenced to one year in jail.

Naproski was convicted last year of McLaughlin's first-degree murder. He could get life in prison without parole when he is sentenced on Jan. 20.