In December of 1966, Myron Lance and Walter Kelbach went on a killing spree that left six dead in about a week.
Kelbach and Lance never did apologize to the families of the victims. Lance died of natural causes in 2010. In August 2018, Kelbach also died of natural causes. He was 80 years old at the time of his death and had served about 51 years in prison. It was one of the longest-running terms ever by a Utah prisoner.
Full story:
https://www.abc4.com/news/the-justice-files-utah-s-first-serial-killers-show-no-remorse/1763159904