&gt;<i>Is there any evidence that criminals conduct more criminal activity during their prison sentence than the general populace? </i><p>The point is rather moot, considering that one of the main purposes of incarceration is incapacitation (effect of a sentence in positively preventing, rather than merely deterring, future offending).<p>I.e. you cannot steal, rob or kill because being monitored in prison prevents you from doing so. Lack of evidence therefore wouldn&#x27;t make much of a justification for removing such monitoring because it could be argued just to show that the monitoring works.<p>However, without digging into statistics I would expect that there is more crime in prisons than outside (not because incapacitation wouldn&#x27;t work at all, but because offenders are concentrated in prison).<p>There is substantial violence in prisons between inmates. (Not only in the US but everywhere).