The Will County Sheriff's Department identified him as the victims' son-in law and said he may have been angry about his divorce from the victims' daughter.
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The suspect was due to report to jail Friday for domestic battery.
Officers found him, his 66-year-old mother-in-law and her 68-year-old husband all suffering multiple stab wounds inside a home Thursday night.
The three were taken to the hospital in critical condition. The woman has been released from the hospital, but her husband and the suspect remain in critical condition.
Police believe this was a domestic incident and there is no wider threat to the public. The incident has troubled neighbors.
"We've been here for 43 years approximately and it's shocking," neighbor Jim Murphy said.
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"My heart broke," neighbor Betsy Hausenschild. "I couldn't do anything but sob through the neighborhood...It's so sad. It's so horribly sad and they didn't deserve this."
Police said it appears a gun may have been fired both inside and outside the home, but it was not clear if anyone had been struck with gunfire.
The couple was taken to a local hospital and then transferred to a Chicago hospital for additional treatment, all in critical condition, police said. The 36-year-old man was airlifted to a Chicago hospital for treatment.
Police said they believe the couple will survive their injuries.
"I've never seen any difficulties over there," Murphy said. "I see George in the morning often times where he's pulling out of the driveway around 6 o'clock. I don't know if he's going to look after his grandchildren. He did say he worked at a food pantry in the area."
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The woman, neighbors said, is a retired teacher. They describe the couple as good people, who were seen walking in the neighborhood almost every day.
Hauenschild paid her respects Friday morning, hoping they recover soon.
"I wanted to pray before their house for them," Hauenschild said. "Because they are a wonderfully sweet and kind couple. I just always enjoyed seeing them always. It was always a pleasure."
The investigation remains active and ongoing, and police are working with other local and state police agencies to attempt to locate other family members and check on their welfare.