Drew Peterson's sons subpoenaed

BOLINGBROOK, Ill., Feb. 28 (UPI) -- Drew Peterson's sons by his third wife have been called to testify in an Illinois grand jury investigation of their mother's death, it was reported Thursday.

The two teenagers, Tom, 15, and Christopher, 13, were granted immunity in exchange for their testimony, ABC News reported.

The boys are living with their father, a former police officer in Bolingbrook, Ill., whose third wife, Kathleen Savio, was found dead in a dry bathtub in 2004 a few weeks before the couple's divorce was to be completed. The death was originally ruled an accidental drowning, but a medical examiner ruled last week after her body was exhumed and autopsied that she was a homicide victim.

Peterson's fourth wife, Stacey Peterson, disappeared last year. Peterson has denied killing either woman and maintains that his fourth wife left him for another man.

Peterson has not been charged with any crime.

Jim Pretto, a member of the grand jury that investigated Savio's death in 2004 said regrets the jury's findings.

"If we would have come back with murder instead, maybe Stacey Peterson would still be here today," Pretto told ABC News. "There is a little bit of guilt that because of that, maybe somebody else was murdered ... that maybe could have been stopped."