Part of it is honestly down to personal preference and the sort of impression one wants to give off with regards to the crime in question - whether you want to be hard on drugs or particular sorts of violence for political reasons, for example. Which isn't the nicest of things, granted, but it does happen and everyone knows it.

Otherwise, it's a matter of what was done and the intent behind it; more or less what one would expect, really. Accidental death warrants more leniency than deliberate negligence, that sort of thing.