MADISON, Wis. (AP) – A North Dakota construction worker has pleaded not guilty by reason of mental disease and defect to killing his three young daughters in River Falls.  Aaron Schaffhausen faces three counts of first-degree intentional homicide and one count of attempted arson in connection with the July deaths of his daughters, 11-year-old Amara, 8-year-old Sophie and 5-year-old Cecilia.  Police discovered all three girls tucked into their beds with their throats slit in July. Prosecutors say Schaffhausen killed the girls to hurt his ex-wife.  A St. Croix County judge entered not guilty pleas on all four charges for Schaffhausen in August. Schaffhausen’s attorney, John Kucinski, filed the mental disease pleas on Wednesday. Schaffhausen’s trail is set for April.