MANDAN, N.D.—A man convicted of killing four people in what authorities say was one of the most gruesome crimes in North Dakota history was sentenced Tuesday to multiple life prison terms without the possibility of parole. South Central District Judge David Reich sentenced Chad Isaak, 47, to consecutive life terms for each of his four murder convictions. One of Isaak’s lawyers had asked Reich to allow for the possibility of parole. Isaak, wearing a blue mask, stood still and stared straight ahead as the judge delivered his verdicts. Before learning his fate, Isaak briefly addressed the court, saying, “I can honestly tell you I’m not a murderer, and that’s all I have to say.” A jury in August found Isaak guilty of killing RJR Maintenance and Management co-owner Robert Fakler, 52; and employees Adam Fuehrer, 42; Bill Cobb, 50; and his wife, Lois Cobb, 45. The four were shot and …