Inside Look at Mercedes Killer's Defense

March 6 -- From the moment he took on the case, defense attorney George Parnham knew that defending Clara Harris would be uphill work.

Harris, a 45-year-old Houston dentist, was accused of killing her cheating husband by running him over with her Mercedes in a hotel parking lot — in front of half a dozen witnesses.

"This is going to be a hard case," Parnham told Primetime 2 ½ months before the trial.

Parnham and Harris gave ABCNEWS extraordinary access to her legal defense, allowing Primetime's cameras to film the defense team's strategy sessions, their meetings with experts, and a mock trial in which they tested their case on a group of stand-in "jurors."

Confrontation at a Hotel

In the statement she gave to police on the night of her husband's death in July 2002, Harris was at times barely coherent, talking nonstop about dental practices and her desire to remake herself for her husband after he told her he was seeing another woman.

She told Parnham that a week earlier her husband, 44-year-old orthodontist David Harris, had revealed he was having an affair with his receptionist, 39-year-old Gail Bridges. She said she tried to save their 10-year marriage by quitting her job, cooking her husband's favorite meals and promising to please him sexually, and that he promised to break up with Bridges over dinner.

She said she checked local restaurants to see if he was keeping his word, but instead caught him and Bridges coming down from a room at the Nassau Bay Hilton, hand in hand. She said she became upset, she got into her car and drove toward Bridges' black Lincoln Navigator, but did not remember running over her husband.

Although Texas law does not allow temporary insanity defenses, Parnham believed he could show that Harris acted under "sudden passion" rather than with intent to kill. While the sentence for intentional murder in Texas is 20 years to life, murder in sudden passion carries a minimum penalty of just two years, with a maximum of 20 years.

Mock Jurors Find Harris’ Account Convincing

On Jan. 5, two weeks before the trial, the defense team convened 20 people as a mock jury. Many of the mock jurors said that judging from what they had heard in the media, they believed Harris had killed her husband intentionally.

The defense team also found that some of the women were quick to judge Harris by her appearance. "Even before she opens her mouth, she has that — that Leona Helmsley look — her type of dress, that much makeup," one woman said, referring to the real estate "Queen of Mean" jailed in the 1990s for tax evasion.

Trial consultant Robert Hirschhorn, whom Parnham had hired to help him pick a winning jury for Harris, said the defense team needed to working on "softening her up."

Next, the defense team showed the panel a videotape they had made of Harris talking about the night of the killing. She admitted grabbing Bridges' hair when she saw her come out of the elevator with her husband, and said hotel employees broke up the fight and steered her toward her car in the parking lot. She said she remembered one of them telling her, "Don't go where they're going."