Monge, a Denver, Colorado salesman, was a native of Puerto Rico who grew up in New York. He was convicted and sentenced to death for murdering his pregnant wife, Leonarda, and three of the couple's ten children after his wife had discovered his incestuous relationship with one of their daughters. Monge's murder victims were: Leonarda, Alan (aged 6), Vincent (aged 4), and Teresa (11 months old). Immediately after the four murders, Monge called police and admitted his guilt.
He had no prior felony convictions; in 1961, however, he abandoned his family for two months and served a short jail sentence in Louisiana for vagrancy. The alleged motive for the murders was "to prevent exposure of sex crimes committed by defendant with his own children". He beat his wife to death with a steel bar as she slept, stabbed Teresa, choked Vincent, and bludgeoned Alan with the steel bar.
After Monge had pleaded not guilty by reason of insanity, psychiatrists evaluated him and found him to be sane. He then insisted on pleading guilty to first-degree murder. A jury that was convened for the penalty phase of the trial recommended a death sentence, and Monge's conviction and sentence were affirmed on appeal. In January 1966, Governor John Arthur Love suspended all executions in Colorado, pending a referendum on capital punishment by voters. On November 8, 1966, the voters decided to retain the death penalty by a three-to-one margin. In March 1967, Monge attracted national attention when he asked a Denver court to allow him to be hanged at high noon on the front steps of the Denver City and County Building. This request was denied.
The following month, Monge fired his attorneys and directed that no attempts should be made to save his life. He gave up all of his appeals and asked to be executed. Nonetheless, his surviving children appealed for clemency. Doctors again evaluated Monge's mental status and found him mentally competent for execution. A week before his death, Monge shared a final meal with his surviving seven children. On the eve of the execution, some seventy members of the Colorado Council to Abolish Capital Punishment gathered on the steps of the state capitol building in Denver in a rally to protest the execution. On June 2, 1967, Monge was executed at the age of 48 in the state's gas chamber. Upon his death, and according to his wishes, one of Monge's corneas was transplanted to a teenaged reformatory inmate.
Monge was buried in Greenwood Pioneer Cemetery in Cañon City, Colorado in the pauper's section set aside for deceased inmates of the state penitentiary. His grave lies a few feet from that of John Bizup, Jr., a convicted murderer executed in 1964. The metal marker indicating Monge's grave has been marred with bullet holes. The Colorado gas chamber, retired after Monge's execution, is now an exhibit at the Museum of Colorado Prisons in Cañon City.
Opponents of capital punishment, in an attempt to abolish the death penalty, waged a national litigation campaign that ultimately found its way to the Supreme Court of the United States. The Court agreed to review a series of cases challenging that the death penalty was unconstitutional. While the Supreme Court reviewed these cases, lower courts in all states stayed all pending executions, thereby creating a de facto moratorium on death sentences throughout the nation. The period of this "unofficial" moratorium on capital punishment began on June 2, 1967, with the execution of Luis Monge in Colorado. It would end nearly ten years later on January 17, 1977, with the execution of Gary Gilmore in Utah.
Luis Jose Monge's was the last execution both in Colorado and in the United States prior to the 1972 Supreme Court decision in Furman v. Georgia. It would be ten full years before any state would carry out another execution and 30 years before Colorado itself would do so. Monge's was one of only two executions to occur in the United States in 1967. His was also the last execution by gas chamber in Colorado.