What do you mean by 'law of the jungle'?
Yeah, a source for the statistics would be nice. And the methods of collecting such data aren't the best - I heartily dislike asking people about what they are like, because I know from my own answers to such questionnaires that I either don't know what I'm like, don't fit any category presented, or am inclined to paint myself in what I perceive as slightly more favourable colours than my real ones. I doubt most people perform any better in filling surveys.
Also, I suspect that the strikingly low ratio of atheists among prison-dwellers isn't in a causal relationship with their atheism at all - for example, if the proportion of atheists is higher among the more educated and most criminals come from the less educated strata of society, you'll see a disproportionately low number of atheists in prison. And conversely with various sorts of theists. Or perhaps many people seek a god after (because) they are imprisoned. So many factors come into play in this sort of investigation, it's really difficult to tease them apart. And I'm not even sure that the difference in the percentages of Christians in the general population and the prison population is significant.
On the other hand, if Christianity somehow prevented people from being bad guys then the expectation would indeed be a disproportionately low number of Christians in the prison population (unless there is widespread post-imprisonment converting) - of which these stats show quite the opposite.
BTW, this:
stands accused of being a
No True Scotsman.