Luis Monge , gassed on June 2 , 1967 , was the last person put to death in Colorado prior to 1977 . One other notable execution was the case of Jack Gilbert Graham who was executed on January 11 , 1957 for killing 44 people by placing a bomb aboard United Airlines Flight 629 . Colorado is notable for being the last state to make use of lethal gas prior to the 1972 Supreme Court decision that effectively abolished capital punishment in the United States . Colorado performed the last pre - '' Furman '' gassing in 1967 . Oklahoma performed the last pre - '' Furman '' electrocution in 1966 . Kansas performed the last pre - '' Furman '' hanging in 1965 . Utah performed the last pre - '' Furman '' execution of a death sentence by firing squad in 1960 ( and coincidentally , the first post - '' Furman '' execution by firing squad in 1977 )
United Airlines Flight 629
United Airlines Flight 629
Capital punishment in Colorado