There are two problems with that:

1. I don't think the data actually exists. The commonly cited figure of 0.2% atheists is extremely dubious.

2. There are too many confounding factors and hidden variables. A plurality of Hindus speak Hindi, but believing in Hinduism neither causes, nor is caused by speaking Hindi. Likewise, if atheists are underrepresented in prisons, there are just too many simple demographic explanations to draw any conclusions about morality.

Be careful when trying to untangle correlation and causation: it may well be that poor people and criminals are more likely to turn to religion. After all, atheism is mainly found in more educated populations.

You don't want to be an outlier in the prison system. If you're not on board with everyone else, there is a real possibility that you're going to get hurt. I think this is part of the reason Atheists are so underrepresented in the prison population. Simple self-preservation.

Care to provide a reference to some numbers for the lazy folks like me? ;).