They say the woman was leaving a gymnastics class with her 10-year-old daughter when the attacker stopped them at the mall in Clay at about 9 p.m. Thursday.
Troopers say 29-year-old David Renz raped the girl and killed the woman in the Syracuse suburb. The girl managed to escape.
Trooper Jack Keller said Friday that the woman died Thursday night and the child is hospitalized.
Renz, of Cicero, has been charged with murder, rape and kidnapping. It wasn't initially known if he has a lawyer.
The Associated Press doesn't publish information that could identify potential sex-crime victims and isn't naming the woman to protect the child's identity.