I think we tend to like to forget that we each have the potential
for abhorrent behaviour. The motivations behind so called 'sinful' actions are very complex, and nothing occurs in a vacuum. Once one is able see, even a little tiny bit, that had they themselves, let's say, had the same upbringing and life conditions of that guy behind bars, that they could have ended up committing some sort of similar sin and wound up in the same circumstances, then compassion
naturally comes in to fill that tiny bit of space left open.