Adams County District Attorney Dave Young said Wednesday after a closed hearing that the boy was charged with first-degree murder with intent to kill after deliberation, and first-degree murder of a child under 12 by someone in a position of trust.
Young said he intends to prosecute the boy as an adult. Authorities have not released the boy's name.
Kiaya Campbell of Thornton was found dead on June 8 about a mile and a half from her father's home in Thornton after her family reported her missing the previous night.
Kiaya had last been seen with the 15-year-old son of her father's girlfriend walking to a shopping center. Police would not confirm if the boy arrested Saturday night was the same one who reported he and the girl had gotten separated during a thunderstorm on June 7.
Investigators said her body had signs of severe trauma, and a local coroner tells CBS Denver the death was not accidental.
More information on her cause of death hasn't been released.