Content warning: This updated story contains new, graphic details of how Vance Boelter killed Melissa Hortman. Vance Boelter pleaded guilty Thursday to murder, stalking and firearms crimes in connection with the killings of former Minnesota DFL House Speaker Melissa Hortman and her husband, Mark, as well an attack on DFL state Sen. John Hoffman and his wife, Yvette, and their daughter, Hope, a year ago Sunday.