The shooting happened at about 8:05 a.m. in the 2100-block of S. Trumbull Avenue in the Little Village neighborhood, police said.
A 25-year-old was inside a house when police said he got into an argument with an unknown man.
The man pulled out a gun and shot the 25-year-old in the chest three times.
The victim was taken to Mt. Sinai Hospital, where he died.
Nobody is in custody.
Area Four detectives are investigating.
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