The boy in Arizona was no stranger to weapons — his father, an avid hunter, reportedly trained his son to shoot prairie dogs — and psychologists said that might have played a role.

An 8-year-old Arizona boy charged with premeditated murder in the deaths of his father and another man shot each victim at least four times with a .22-caliber rifle, methodically stopping and reloading as he killed them, prosecutors said Monday.

Although investigators initially said they thought the boy might have suffered severe physical or sexual trauma, they have found no evidence of abuse, said Roy Melnick, the police chief in St. Johns, Ariz., where the shootings occurred. Psychologists say such abuse is often a factor in the extremely rare instances in which a small child murders a parent.