Updated

A doctor goes on trial Thursday on charges that he killed his wife in their Utah home with a fatal dose of prescription drugs in what prosecutors say was a twisted plot to carry on an affair with his mistress.

A jury was seated Wednesday, setting the stage for opening arguments in the sensational case.

Martin MacNeill, 57, was charged in August 2012, nearly five years after his former beauty queen wife was found in a bathtub at the couple's Pleasant Grove home, about 35 miles south of Salt Lake City.

Prosecutors will try to prove that MacNeill gave his wife a lethal combination of drugs while having an affair with a woman named Gypsy Willis. Investigators have said MacNeill hounded his wife to get a face-lift, then persuaded the plastic surgeon to prescribe the potent mix of pills for her recovery.

The state's case is anything but certain. Medical examiners couldn't determine how 50-year-old Michele MacNeill died. They initially ruled she died of natural causes, possibly from a heart disorder, then changed the finding to undetermined.

The trial before 4th District Court Judge Derek Pullan is expected to last six weeks.

The MacNeills had eight children, and their oldest daughters have been outspoken in their belief that their father killed their mother. Rachel MacNeill and Alexis Somers have gone on national TV with their claims and sat in his court hearings holding up photographs of their mother. They insist his motive was an affair with the woman he later moved into his home.

The doctor later went to prison on fraud charges, and it wasn't until his release that prosecutors moved to file charges of murder and obstruction of justice.

The woman with whom he allegedly had an affair also served prison time for fraud. The allegations included forging a document that said they were married on April 14, 2007 — the day of Michele MacNeill's funeral.