Drew Peterson's two sons with third wife Kathleen Savio are expected to appear Thursday morning before a grand jury investigating the death of their mother, FOX News' Greta Van Susteren reported.

Sources close to the Peterson investigation told Van Susteren four police officers arrived at the ex-police sergeant's house at 9 a.m. Wednesday.

Peterson answered the door and they asked to see 13-year-old Christopher and 15-year-old Tom.

When they came to the door, police served them each with a grand jury subpoenas.

The 54-year-old former Bolingbrook police officer has been named a suspect in his fourth wife Stacy Peterson's October disappearance, but hasn't been charged with any crime and denies having anything to do with her disappearance.

Last week, a coroner ruled Peterson's third wife, Kathleen Savio, died by drowning and her death was ruled a homicide. She was found dead in her bathtub in March 2004, shortly before her divorce with Peterson was finalized. Four years ago, a coroner's jury ruled her death was an accident.

Peterson is reportedly attempting to hire a lawyer for the two boys.

FOX News' Greta Van Susteren contributed to this report.