Only that it is exceedingly rare. Proof "beyond a reasonable doubt" is a very demanding standard, and is not even shared by all countries in the west, much less the rest of the world. Talk to any prosecutor and you will be assured that, notwithstanding the popular narrative, many, many more guilty people go free in the US than the other way around. But in any event, to the degree there are those who are wrongfully imprisoned, I cannot imagine that supporting an argument that other prisoners should somehow be treated better.