A 22-year-old man entered a not-guilty plea after he was charged with fatally stabbing his 7-year-old niece.

WSIL-TV reports Justin DeRyke was formally arraigned Thursday on three counts of first-degree murder.

He was charged Wednesday with the slaying of Willow Long, who was killed earlier this month near her family's home in Watson, a village about 100 miles northeast of St. Louis.

Investigators say DeRyke insisted he killed his niece to "put her out of her misery" after he says she fell onto a brush pile and pierced her neck with a stick.

Prosecutors say they're seeking a life sentence for DeRyke, who was represented by a public defender.

He's being held on $5 million bond and is set to appear again in court on Oct. 22.