ST. LOUIS, MO - A woman has been sentenced to prison for killing her 16-year-old girlfriend during a game of Russian roulette. On Thursday, October 16, Mary Lashawn Cornelius, 19, was sentenced to seven years in prison for first-degree involuntary manslaughter in the death of 16-year-old Mattison Johnson.
The seven year sentence was part of a plea agreement with prosecutors, which in turn dropped the armed criminal action charge, KSDK reported. Prosecutors said that Johnson was killed on January 3, 2025, in a home on the 1400 block of East Grand Boulevard. Police said they found Johnson bleeding from a head wound on the living room floor. They also said Cornelius was in the same room.
In court on Thursday, Cornelius admitted to playing with the gun and "accidentally" shooting Johnson in the head, saying that the two of them were playing Russian roulette. Johnson's mother, Nicole Pettis, said she believes the two girls were dating. "The judge asked Mary point blank, who put the bullet in the gun, and she said, 'I don't know,'" shared Pettis.
Pettis said she also did not know that the two girls were playing Russian roulette in her home. Pettis previously said that her nine and 11-year old daughters were home when the shooting happened. "It was my nine-year-old daughter. She said, 'Mommy, you got to get home.' I couldn't even really understand her, but she was hysterical. She said, 'Mommy, Matti was shot,'" Pettis recalled.
She said she is proud that her two younger daughters had the courage to be in court and face the defendant. "I'm not even sure that my daughters know what Russian roulette is but I think it was just a trigger for them because they did talk about her essentially spinning the gun around her finger and I guess that's apparently when the trigger was pulled and the gun killed my daughter essentially," Pettis said.
Prosecutors described the shooting as a case of Cornelius negligently handling the firearm, but Pettis previously said she believed the shooting wasn't an accident, as she said the relationship between her daughter and Cornelius was abusive.
"I will get justice for my daughter," said Pettis when Cornelius was first charged in the case. "I don't want to see anything bad happen to her besides sit behind bars, think about it for the rest of your life, hold that image in your head for the rest of your life of what you did to my daughter. I hope that she haunts you, God forgive me, but I hope that my daughter eats her alive every night when she goes to bed."
In court on Thursday, a friend of Johnson's family said that Johnson's mother and two daughters are still struggling over Johnson's death and that an apology wouldn't change anything. "Nothing is a game when it comes to gun," she said.
Cornelius' sister offered an apology on Cornelius' behalf, saying her sister made a terrible mistake. "A child is gone, so you'll have to take responsibility," she said. While in court, Pettis wore a shirt that read, "Never and accident ... guns aren't toys." It's a design she created herself.
"She was kind, bubbly, generous, energetic, always the life of the party, Pettis said about her daughter. She said she will always remember the happy moments as she continues to grieve her daughter.
The seven year sentence was part of a plea agreement with prosecutors, which in turn dropped the armed criminal action charge, KSDK reported. Prosecutors said that Johnson was killed on January 3, 2025, in a home on the 1400 block of East Grand Boulevard. Police said they found Johnson bleeding from a head wound on the living room floor. They also said Cornelius was in the same room.
In court on Thursday, Cornelius admitted to playing with the gun and "accidentally" shooting Johnson in the head, saying that the two of them were playing Russian roulette. Johnson's mother, Nicole Pettis, said she believes the two girls were dating. "The judge asked Mary point blank, who put the bullet in the gun, and she said, 'I don't know,'" shared Pettis.
Pettis said she also did not know that the two girls were playing Russian roulette in her home. Pettis previously said that her nine and 11-year old daughters were home when the shooting happened. "It was my nine-year-old daughter. She said, 'Mommy, you got to get home.' I couldn't even really understand her, but she was hysterical. She said, 'Mommy, Matti was shot,'" Pettis recalled.
She said she is proud that her two younger daughters had the courage to be in court and face the defendant. "I'm not even sure that my daughters know what Russian roulette is but I think it was just a trigger for them because they did talk about her essentially spinning the gun around her finger and I guess that's apparently when the trigger was pulled and the gun killed my daughter essentially," Pettis said.
Prosecutors described the shooting as a case of Cornelius negligently handling the firearm, but Pettis previously said she believed the shooting wasn't an accident, as she said the relationship between her daughter and Cornelius was abusive.
"I will get justice for my daughter," said Pettis when Cornelius was first charged in the case. "I don't want to see anything bad happen to her besides sit behind bars, think about it for the rest of your life, hold that image in your head for the rest of your life of what you did to my daughter. I hope that she haunts you, God forgive me, but I hope that my daughter eats her alive every night when she goes to bed."
In court on Thursday, a friend of Johnson's family said that Johnson's mother and two daughters are still struggling over Johnson's death and that an apology wouldn't change anything. "Nothing is a game when it comes to gun," she said.
Cornelius' sister offered an apology on Cornelius' behalf, saying her sister made a terrible mistake. "A child is gone, so you'll have to take responsibility," she said. While in court, Pettis wore a shirt that read, "Never and accident ... guns aren't toys." It's a design she created herself.
"She was kind, bubbly, generous, energetic, always the life of the party, Pettis said about her daughter. She said she will always remember the happy moments as she continues to grieve her daughter.
For corrections or revisions, click here.
The opinions reflected in this article are not necessarily the opinions of LET
Comments
2025-10-22T22:31-0400 | Comment by: James
Seven years IS NOT justice! These courts and justice systems are a joke!