St. Petersburg police identified the victim as Paris Hamilton, the St. Petersburg Times reported. No suspects were in custody.
Police said they suspect the shooting may have been an act of retaliation, though they didn't disclose the basis for that suspicion.
A semiautomatic rifle was used to fire into the house where Hamilton was sleeping in the front room, the newspaper said. Police said the girl lived in the home with her legal guardian, Shenita Joseph, since her mother died several years ago.
The Times said Joseph was home at the time of the shooting, along with several other adults and a second child.
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