(CBS) EFFINGHAM, Ill. - Justin DeRyke, the uncle of Willow Long, a 7-year-old Illinois girl who was found dead Monday night, was charged Wednesday with three counts of first-degree murder in her death and was ordered held on $5 million bond, CBS St. Louis reports.

A criminal complaint alleges the 22-year-old DeRyke stabbed his niece in the chest with a knife on the family's property Saturday night.

DeRyke told investigators he was home alone with Willow and her three-year-old brother Saturday night when Willow accidentally scratched him, according to court documents obtained by the station. This reportedly angered him and caused him to yell at Willow which in turn led her to run out of the house and towards a brush pile in the family's backyard.

DeRyke said he chased after her, but she tripped and fell into the brush pile causing a stick to impale her neck, the station reports, according to the documents.

DeRyke reportedly told police Willow began to twitch and he believed he had to end her suffering, so he grabbed a knife out of his bedroom, slit her throat and then stabbed her in the heart approximately five times.

According to court documents, DeRyke then told police he put Willow's body into several plastic bags and secured the bags with duct tape. Afterwards, DeRyke said he disposed Willow's body in a rural area south of Watson, Illinois.

Volunteers discovered Willow's body around 7:30 p.m. Monday and DeRyke was arrested around 6 a.m. Tuesday.

An autopsy conducted Tuesday on the girl revealed that her throat had been slashed. Smaller stab wounds were also discovered near her collarbone and neck. Doctors also found defensive wounds on Willow's hands, according to the station.

Complete coverage of Willow Long on Crimesider