HASTINGS, Neb.–The mother of a slain 4-year-old Hastings boy and her live-in boyfriend have pleaded not guilty to charges of child abuse resulting in death.

29-year-old Amanda Pecor and 30-year-old Matthew Edwards made their plea Thursday in Adams County District Court. Police say the Pecor’s 9-year-old son fatally shot his 4-year-old brother, Beau Pecor, on April 18.

Prosecutors say police, school and mental health officials had concerns about the 9-year-old’s often violent behavior. Prosecutors say officials had warned both Pecor and Edwards in the weeks before the shooting not to have guns in the house and to lock up all knives and other sharp objects.