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The judge in Drew Peterson's murder trial handed prosecutors a legal victory Tuesday by giving them the go-ahead to introduce evidence in coming days that the former suburban Chicago police officer sought to hire a hit man to kill his third wife.

Prosecutors allege Peterson, now 58, ended up killing his third wife, Kathleen Savio, himself in 2004. They want to bring up the hit-man evidence in an effort to demonstrate Peterson had thought about killing Savio for at least months before she died.

Attorneys for the state didn't list the hit-man allegation on appropriate pre-trial documents -- apparently as an oversight -- and defense attorneys had argued prosecutors shouldn't be allowed to correct that mistake a month into the trial.

Also Tuesday, pathologist Mary Chase testified that a 2-inch gash on the back of Savio's head could not have caused her to pass out. Her testimony countered defense suggestions that Savio slipped in her bathtub, hit her head, lost consciousness and drowned.

As Case spoke, prosecutors projected autopsy photos of Savio's head with the top half of her skull cut away. Some jurors shifted in their seats.

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The head wound penetrated the thick layer of skin around the skull, Case told jurors, but caused no damage to the brain.

"There was no brain trauma ... no internal brain injury that would have caused a loss of consciousness," Case said.

Case is one of several forensic experts to testify as prosecutors seek to prove that Savio was murdered. Her death was initially ruled an accident but was reclassified a homicide in 2007 after Peterson's fourth wife, Stacy Peterson, went missing in 2007. Peterson, a former Bolingbrook sergeant, is a suspect in his fourth wife's disappearance but hasn't been charged in her case.

Case said Savio would have had to fall hard three separate times to account for deep bruises on the front of her body and the injury to the back of her head. But the judge upheld a defense objection about that comment and told jurors to disregard it.

Prosecutors have no physical evidence tying Peterson to Savio's death, so they have endeavored to build a circumstantial case against Peterson, who has pleaded not guilty to first-degree murder. Prosecutors hope jurors will conclude that the only plausible explanation for Savio's death is that Peterson killed her.

The hit-man testimony could help make that argument.

Judge Edward Burmila previously had not allowed the hit-man allegation to be raised in front of jurors, but he ruled Tuesday that prosecutors could introduce the evidence for a narrow purpose.

"The issue is not whether he wanted to hire a hit man," he said. "The issue is: Did the defendant intend to kill his wife? ... This evidence goes to that matter."

When lead prosecutor James Glasgow touched on the hit-man accusation in his opening statement, the defense asked for a mistrial. At the time, Burmila agreed the state shouldn't have strayed into that topic and he told jurors to disregard it.

Burmila's ruling on Tuesday means prosecutors can call as a witness Jeff Pacther, who worked with Peterson at a cable company where he moonlighted. Pachter previously accused Peterson of offering him $25,000 in late 2003 to hire a killer.

At a 2010 hearing, Pachter testified that -- as the two rode in Peterson's squad car -- Peterson asked if he could find someone to "have his third wife taken care of." Pachter said he took that to mean he wanted her murdered, though Peterson didn't use that word.

Pachter said he didn't take Peterson's offer seriously, saying he simply responded, "OK," but did nothing about it.

Pachter hadn't heard about Savio's death in March 2004 until he telephoned Peterson the following July about another matter. He said Peterson told him during the call that, "By the way, the favor that I asked you, I don't need it anymore."