The shooting happened in the 10200-block of South Ewing Avenue in the East Side neighborhood after 5:30 p.m., police said.
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A 22 year-old man, 17-year-old boy and 24-year-old woman broke into the home through the basement, police said. The man has been identified to the Cook County Medical Examiner's Office as Narcisco Ledesman. The identities of the boy and woman who were killed have not been released.
A man in his 30s who lives in the home with his family and has a valid firearm owners' identification card saw the burglars and shot them all dead, police said. He then apparently locked himself in a room while he called police.
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"I passed by and I had seen all the police in front of his house, so I went and parked my truck down the block and I walked over here with my girlfriend and I told her I know something is bad because they're all in front of his house," said Havi Real, a friend of the homeowner.
No charges have been filed against the homeowner, but police are still trying to confirm his account.
"We have noticed inconsistencies in his story and detectives are continuing to investigate," police spokesman Anthony Guglielmi said Monday morning.
"We're in the middle of the interrogation," Guglielmi said, noting that he could not share any additional details. "We're pressing pretty hard."
Sun-Times Media Wire contributed to this story