Yes there are plenty of atheists in jail as well as alot of cons pretending to be born again Christians in order to get early released/parole etc. People in jail are desperate to get out and will say and do what it takes to get out. Worked with plenty of inmates who dont believe in God and tend to live a life with the devil. Thats why they are in that mess. Lots of inmates that are good people who made mistakes but they believed in God before they went to jail.

From my experience in Corrections for 18years, there are plenty of atheists in jail.