Scott Peterson's former mistress -- the prosecution's star witness -- may take the stand Tuesday at his double murder trial. Amber Frey's (fryz) attorney Gloria Allred says she expects Frey to be on the stand "a considerable amount of time." But first, the court is expected to resolve the issue of some recently discovered evidence that defense attorneys say could point suspicion away from Peterson. Defense attorney Mark Geragos says preliminary test results on the evidence could be available Tuesday. Prosecutors allege Peterson killed his pregnant wife in their Modesto, California, home around December 24th, 2002, and then drove to the San Francisco Bay and dumped her body from a small boat. They've sought to show Peterson's affair with Frey, and hopes for financial gain, were his motives to kill his pregnant wife, Laci.