By Joseph Hosey

JOLIET, Illinois (Reuters) - Defense attorneys will decide by Thursday morning whether to pursue a request for a mistrial for former Chicago-area police officer Drew Peterson, who is charged with killing his third wife.

The defense asked for a mistrial on Wednesday, saying the prosecution had improperly introduced evidence.

It was the second mistrial request in as many days in the murder trial before Will County Judge Edward Burmila. Defense lawyers want the charges against Peterson dropped and the judge to declare he cannot be retried on them.

Burmila said he was loath to declare a mistrial, and asked Peterson's lawyers if they would accept striking all or part of testimony given on Tuesday by Peterson's former next-door neighbor, Thomas Pontarelli. Defense attorneys said they would give their decision in the morning.

Pontarelli testified that he found a .38-caliber cartridge nose-up on his driveway in 2002, which he believed Peterson had placed there to intimidate him.

Defense attorneys said that because there was no proof Peterson put the bullet there, prosecutors should not have elicited the testimony.

The judge said eliciting the testimony was a "low blow."

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 Lifetime television network movie "Untouchable" starring Rob Lowe as Drew Peterson. His first and second wives have remarried.

Pontarelli testified on Tuesday he was intimidated by Peterson, who had learned that Pontarelli had helped Peterson's estranged wife, Savio, move things out of her house.

Peterson also had suspected Pontarelli had changed the locks on Savio's front door, although he had not changed the locks, Pontarelli testified.

LITTLE PHYSICAL EVIDENCE

Defense attorney Steve Greenberg objected when Pontarelli testified about finding the cartridge, saying prosecutors were introducing "prior bad acts" and attempting to "dirty up Mr. Peterson."

Burmila questioned prosecutor Kathleen Patton on the bullet testimony. Patton said prosecutors had sought to show jurors that Pontarelli and Peterson were not friends. Peterson has denied putting the bullet in the driveway.

The judge on Tuesday denied a defense request for a mistrial after Will County State's Attorney James Glasgow told jurors in an opening statement that a man Peterson worked with at a cable television installation company had said under oath that Peterson offered him $25,000 to find a hit man to kill Savio.

Burmila ruled that prosecutors could not use testimony from the man.

The testimony of family, friends and associates is key to the prosecution case against Peterson because there is little physical evidence tying him to Savio's death.

(Editing by David Bailey, Greg McCune, Mary Wisniewski and Peter Cooney)