Charges have been upgraded against a Tennessee man in his 3-year-old son's shooting death.

Court document show 25-year-old Cortez Wilkerson now faces charges of first-degree murder and aggravated child neglect in the death of Kash Sharp on Saturday in Memphis. He initially was arrested on reckless homicide and drug and weapons charges in the boy's death and pleaded not guilty Monday.

An affidavit shows Wilkerson now faces the new charges. His lawyer did not immediately return a call seeking comment Tuesday.

Documents show Wilkerson told investigators he was awakened by a gunshot and, when he opened his eyes, he saw his son lying on his lap with a gunshot wound to the head.

Records show investigators later determined Wilkerson was the only one who could have fired the gun.