A woman called Rockford police officers just after noon, saying her 6-year-old daughter told her a man took her 10-year-old sister.
Someone flagged down officers at about 12:40 p.m., telling them he found an unresponsive girl outside a home in the 1200 block of 9th Avenue.
Officers found the child and administered CPR. The Rockford Fire Department transported the girl to a local hospital, where she was pronounced dead.
Police then found a man who matched the suspect description near 9th Street and Woodruff. Officers took the man, later identified as Antonio Monroe, into custody after a brief struggle.
Monroe has been charged with first-degree murder, attempted murder, aggravated battery by strangulation and two counts of kidnapping.