A Missouri teen is headed to prison for killing her 16-year-old girlfriend during a game of Russian roulette , with prosecutors saying she shot the victim in the head while "spinning the gun around her finger," according to her mom.

"That's apparently when the trigger was pulled and the gun killed my daughter essentially," Nicole Pettis, Mattison Johnson's mother, told local NBC affiliate KSDK after Mary Cornelius, 19, was sentenced to seven years in prison Thursday after she pleaded guilty to first-degree involuntary manslaughter .

Johnson's two young sisters, ages 9 and 11, were with the two teens when the shooting occurred at their home on Jan. 3, with one of them finding her, Pettis says.

"It was my nine-year-old daughter," Pettis recalled. "She said, 'Mommy, you got to get home'. I

See Full Page