Prosecutors in southeast Missouri have decided not to file charges against a teenager who fatally shot a man who was allegedly holding a knife to his mother's throat.

The Poplar Bluff Daily American Republic reports that authorities determined that Brody Carter of rural Butler County acted in "third-party self-defense" in killing 41-year-old Thomas Sherrion on Sunday at the home that Sherrion shared with Carter and his 55-year-old mother, Connie Diel.

Butler County investigator Wes Popp says Sherrion and Diel were involved in a domestic dispute when Sherrion put a knife to her throat and threatened to kill her.

Popp says Carter went to his bedroom and grabbed a rifle, which he used to shoot Sherrion in the back.