Charles Vacca, 39, was teaching the girl how to use the automatic weapon on Monday morning at the Last Stop outdoor shooting range in White Hills, Arizona, when she pulled the trigger and the kickback caused the gun to lurch over her head, investigators said.
Sam Scarmardo, the manager for the Last Stop's shooting range, told NBC News that "the established practice at most shooting ranges is 8 years old and up with parental supervision."
He said Vacca was a "great guy, with a great sense of humor" and called him "very conscientious and very professional."
Scarmardo said that the range has never had a similar incident in over a decade of being open — "not even a scratch."
"I just ask everybody to pray for Charlie, and pray for the client, she’s going to have a hard time," said Scarmardo.
The Arizona Department of Public Safety referred inquiries to the Bureau of Alcohol Tobacco and Firearms, which didn't return calls for comment.
Ronald Scott, a Phoenix-based firearms safety expert, said most instructors usually have their hands on guns when children are firing high-powered weapons. "You can't give a 9-year-old an Uzi and expect her to control it," Scott told the Associated Press.