The girl's father is dating Ricky Lee Blackwell's estranged wife. Spartanburg County deputies said Blackwell shot the girl twice in the driveway of a home where he had taken her and his estranged wife to swim and play. The home is in Chesnee, about 60 miles southwest of Charlotte, N.C.
Several adults and children saw the shooting and pointed officers toward Blackwell, investigators said.
Blackwell shot himself as police closed in. He was taken to a hospital but his condition wasn't released.
The coroner's office identified the girl as Heather Brooke Center of Woodruff.
Investigators said they weren't sure of Blackwell's motive.
"I don't know where you can go in the mind to justify shooting a child," said Spartanburg County Sheriff Chuck Wright. "I don't understand how you can get so angry."
The sheriff said Blackwell, 50, has a long criminal record. He was charged with murder and kidnapping. No one answered his phone Wednesday night.
"As soon as they called his name, I knew him," Wright said. "I'd heard that boy's name before."