John Granat, 44, and his 42-year-old wife Maria were found beaten to death in their unincorporated Palos Park home on Sunday. On Monday, the Medical Examiner ruled the deaths homicides.
The Cook County Sheriff's office says a person of interest is being questioned.
Police arrived early Sunday morning to the house in the 12700-block of 81st Court after a young male relative inside called 911 to report the deaths.
Neighbors say the Granats lived in the home with their teenage son, and a father of one of the victims may have lived in the home at one time.
On Sunday, investigators questioned the male relative who was found in the home. There are reports that the person of interest is also a male relative.
A spokesman for the Cook County Sheriff's Department said this incident poses no immediate threat to those nearby. Still, neighbors wonder what happened.
"Everybody around here would be kind of nervous not knowing if it was somebody that was related to the family or if it was just a random incident that the police are investigating and don't know," said John Vujevich, neighbor.
"It's so sad," said neighbor Janina Lassak. "The kids go to the same school. They meet at the stop every day and they've got only one son, so I don't know what's happened and how such a crime can happen in this neighborhood."
"It's very unusual. I can't remember the last time I've heard of a murder like this, especially a double homicide, in a quiet neighborhood," said neighbor Cheryl Hoban. "So it was a little disturbing."
No charges have been filed.