This article looks at the religious beliefs of prison inmates and finds that the fraction of those who are non-believers is almost negligible, far smaller than their numbers in the general population.
In “The New Criminology”, Max D. Schlapp and Edward E. Smith say that two generations of statisticians found that the ratio of convicts without religious training is about 1/10 of 1%. W. T. Root, professor of psychology at the Univ. of Pittsburgh, examined 1,916 prisoners and said “Indifference to religion, due to thought, strengthens character,” adding that Unitarians, Agnostics, Atheists and Free-Thinkers are absent from penitentiaries or nearly so.
During 10 years in Sing-Sing, those executed for murder were 65% Catholics, 26% Protestants, 6% Hebrew, 2% Pagan, and less than 1/3 of 1% non-religious.
Just because a person claims to be religious, it doesn’t necessarily mean they live it. There are varying degrees of religiosity out there. Also, did you ever consider the possibility that maybe the people imprisoned might have been atheist/agnostic on the outside and then became religious AFTER they were incarcerated? There are hundreds of prison ministries operating all over the world, and they are effective. Two famous examples: Chuck Colson didn’t become a born again Christian until after he was in prison. Malcolm X became Muslim while in prison. In fact, Islam is one of the fastest growing religions amongst the prison population. One thing about being in prison: it gives a person plenty of time time to think over their lives and deeds and then decide to try to become changed people. I would say that is a positive vs a negative thing. It’s not right to imply somehow that it’s religious practise that put them in prison, nor is it right to attempt to claim that somehow atheists are morally superior to others and can do no wrong.