By Joseph Hosey

JOLIET, Illinois (Reuters) - A judge on Tuesday would not allow testimony to be used from a man who said that former Chicago area policeman Drew Peterson offered him $25,000 to find a hit man to kill Peterson's third wife, dealing a blow to prosecutors on the first day of the murder trial.

Peterson is charged with the murder of third wife Kathleen Savio, who was found dead in a dry bathtub in 2004. Her death initially was ruled an accident. But when Peterson's fourth wife, Stacy Peterson, disappeared in 2007, suspicions were raised and the Savio death was ruled a homicide. Stacy Peterson has never been found and is presumed dead.

The Peterson case has drawn national attention and was the subject of a popular Lifetime television network movie "Untouchable" starring Rob Lowe as Drew Peterson.

Prosecutor James Glasgow began his opening statement on Tuesday by telling the jury that Jeffrey Pachter, a man Peterson worked with at a cable television installation company, has said under oath that Peterson offered him $25,000 to find a hit man to kill Savio.

Defense attorney Steve Greenberg immediately called for a mistrial. Judge Edward Burmila cleared the jury out of the courtroom and allowed Greenberg to make his case for a mistrial.

Burmila rejected the mistrial motion, but ruled that the prosecution could not use anything from Pachter during the trial.

The ruling was a blow to the prosecution because there is little physical evidence to link Peterson to Savio's death and prosecutors hoped to use the testimony of family and associates as evidence of Peterson's guilt.

The judge also admonished defense lawyer Joel Brodsky for launching into a story of Peterson's early life rather than focusing on the facts of the case.

"Mr. Brodsky, you're testifying to the jury about Mr. Peterson's life story, which is completely inappropriate," Burmila said.

Brodsky then focused on Savio's character, calling her a liar who had a nasty temper and had attacked Drew Peterson.

Peterson betrayed no emotion during the morning session of the trial's first day. Before the trial started, a defense team intern helped Peterson knot his tie and smooth his collar.

Peterson's first and second wives have remarried.

(Editing by Greg McCune and Andre Grenon)