The shooting happened at about 12:05 a.m. in the Loop near East Adams Street and South Wabash Avenue, police said.
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Police said the two men were arguing with another man, who was with a woman dressed in all pink. The suspect then pulled out a gun and shot both victims.
One victim, a 37-year-old man, was shot in the chest and was transported by the Chicago Fire Department to Stroger Hospital in critical condition. The other man, 40, was shot in the back and shoulder. He was transported by CFD to Northwestern Hospital in critical condition.
No one is in custody and Area Three detectives are investigating.