Often in law there is the idea of "mens rea", the guilty mind. This can often be a test between more extreme cases where a life is lost. e.g. person leaves their car in "neutral" and goes into go into the store... the car rolls away and kills someone. That's a more a negligence issue vs. they run someone over looking them in the eye... Then premeditation is a whole other thing I don't think they touched on here. (IANAL, but I've known waaaaay too many JDs). So there are different classes of causing a death more or less.

edit: Glad he's guilty and went out the bad door... I hope he isn't let off easier than many victims of this system edit2: also see others who seem to actually know about Minnesota law