77% of US citizens claim to be Christians, which is about the same percentage of those in prison.
A better percentage to know would be what percentage of Christians are in prison, but better still would be to know what percentage of “practicing” Christians are in prison.
We might ask why prisons aren’t populated with only those outside of Christianity–in the remaining 23%, but Christians sin and fail like everyone else. More importantly, I suspect that there is simply an “identification” with Christianity, but that it was abandoned and not practiced by the vast majority of those in prison. Certainly hardened criminals have abandoned their practice of the faith.
Also, being incarcerated might tend to make some introspective and reach out to Christianity for forgivness and salvation, while causing others to feign a conversion for the sake of being let out early.
The comment I wanted to make earlier boils down to seeking that which is within, or other worldly, and it’s due to the harsh realities of being imprisoned.
Religion is particularly attractive in this way, and it is no surprise conversion rates are high.
In some cases it is a good thing. In others it is an escape, easily bent to ill ends.
The UK recently affirmed the right to read, and IMHO doing that resonates with my comments above. Nearly all types of prison come with the option to have religious materials. I find the UK decision notable in that it recognizes our need to seek, understand, experience as a human thing, not just some path to religion.