On Friday the 13th, Christine Markle and her daughters are found murdered. A signed confession points to John Markle, but the blood-stained Halloween mask left at the scene raises haunting questions. Watch “The Friday the 13th Murders” Wednesday on ID. | Investigation Discovery

On Friday the 13th, a teen obsessed with Satan and serial killers unleashed a night of terror in a small Texas town. As dawn broke, the bodies began to surface, and one arrogant suspect led police to a remote hillside where the truth lay buried. Watch "The Friday The 13th Murders" Wednesdays on ID. #TheFridayThe13thMurders | Investigation Discovery