Mistress called back to murder trial of Utah doctor as another inmate testifies against him

A mistress will make a return appearance Thursday at the murder trial of a Utah doctor charged in his wife's largely unexplained death inside a bathtub.

But first, an inmate is set to finish his testimony claiming Martin MacNeill acknowledged drowning his wife.

Prosecutors plan to wrap up their case Thursday by calling back Gypsy Willis, the mistress they say was MacNeill's motive for getting rid of his wife. He's accused of knocking out Michele MacNeill with drugs after cosmetic surgery, then leaving her in the tub.

Defense lawyers argue she died of natural causes. They contend that Michelle MacNeill had a heart attack in 2007 and fell into the tub. A cause of death was never established.

Closing arguments could begin as soon as Friday.