A Missouri woman accused of taking part in the abuse that killed a 4-year-old girl has pleaded guilty to murder and assault, bringing her case closer to a final sentencing more than five years after the child’s death.
Kourtney Taylor Aumen pleaded guilty Monday to second-degree murder and first-degree assault in connection with the December 2020 death of Jessica Joy Mast, according to recent court and local news reports. Her plea came just weeks before the trial was scheduled to begin.
Aumen had previously faced more serious charges, including first-degree murder, child abuse, child endangerment and armed criminal action.
Child found dead inside Missouri home
The case began on Dec. 20, 2020, when Benton County deputies responded to a rural home near Cole Camp following a report involving an unresponsive child.
Inside the home, deputies found Jessica dead on a bedroom floor. She was wrapped in a pink blanket near bunk beds. Investigators reported extensive bruising and open wounds, including injuries consistent with repeated beatings.
Investigators also found evidence that the child had been taken outside to a pond during the winter. Authorities said she was repeatedly forced into the cold water after being beaten. When she was found, her hair was still wet and there was vomit near her body.
The pond incident was part of a larger pattern of alleged abuse involving Jessica and another child, according to court records and investigators.
Investigation pointed to a disturbing belief
Investigators said Aumen and Ethan Mast, a neighbor who was also charged in the case, told Jessica’s parents that the family was dealing with a supposed demonic presence.
According to statements gathered during the investigation, the adults were told that Jessica’s mother had a “demon” inside her and that the children could become like her if the situation was not addressed.
Benton County Sheriff Eric Knox later described what happened as a “religious-type episode.”
Jessica’s parents told investigators they were forced to watch the abuse and were threatened when they tried to intervene. The investigation also found that Jessica’s mother and a 2-year-old boy were subjected to abuse during the same period.
Other defendants have already entered pleas
Aumen was not the only person charged after Jessica’s death.
Ethan Mast previously pleaded guilty in the case. Jessica’s parents, James and Mary Mast, also entered guilty pleas to charges connected to the events surrounding their daughter’s death.
The legal proceedings involving the family have continued for years. James Mast’s case has included additional court filings after his earlier plea, while Mary Mast’s case remains active as well.
Aumen’s case was moved to Webster County on a change of venue in 2025. Her defense also raised questions about her competency during the lengthy proceedings. In September 2026, a court filing indicated that she had again been found competent to proceed.
Sentencing is now scheduled
Aumen’s guilty plea came after her case had been moving toward a jury trial scheduled for Oct. 26.
Instead, the change-of-plea hearing was held Oct. 5, and the murder and assault charges were resolved through her guilty plea.
She is scheduled to return to court for sentencing at 1:30 p.m. on Dec. 21, 2026.
The plea closes one of the major remaining stages in a case that began with the death of a young child in December 2020 and resulted in criminal charges against four adults.
Jessica Mast was 4 years old when she died. Her death and the allegations surrounding the abuse have remained at the center of the case as the courts worked through the charges against those accused of participating in the events.
