Shelly additionally said that there are still some world leaders "who would resort to the death penalty as a 'quick fix' rather than tackling problems at their roots with humane, effective and evidence-based policies."
"Strong leaders execute justice, not people," Shelly continued.
In the belated Pope John Paul II's papal encyclical on life, Evangelium Vitae, the pope affirmed the dignity of human life while also calling for justice for offenses against life. He noted that the death penalty should be "viewed in the context of a system of penal justice ever more in line of human dignity" and "with God's plan for man and society," which should only be used in "cases of absolute necessity." He noted that these cases would be "rare."
Pope Francis has also defended the dignity of every life throughout his papacy and has been an advocate against the death penalty, calling the practice "inhumane."
"No one ought to be deprived not only of life, but also of the chance for a moral and existential redemption that in turn can benefit the community," he said in an address to the Pontifical Council for Promoting the New Evangelization in October 2017.
Currently, there are 21,919 people on death row around the world.
"The death penalty is a symptom of a culture of violence, not a solution to it," Shelly said.
"Over the past 40 years, we've seen a huge positive shift in the global outlook for the death penalty, but more urgent steps need to be taken to stop the horrifying practice of state killing."