SALT LAKE CITY (AP) — A former Utah teacher has pleaded guilty to murder charges in the shooting death of her ex-husband’s girlfriend, who was killed in front of the former couple’s 3-year-old twins. Prosecutors have said Chelsea Cook shot Lisa Williams while Williams and the children decorated a Christmas tree in 2018. Cook pleaded guilty Friday to aggravated murder and other charges in an agreement with prosecutors. The Williams family has said Cook harassed the 26-year-old online and in person for months before the slaying. Cook was a high school health teacher in Lehi before her arrest.