It means that Murray has been charged with Involuntary Manslaughter and that he can maximum get 4 years of jail time. If he plea bargain, he can get off completely without jail time or he will serve about a 6 months to a year. If he is convicted he will serve (with Good Behavior) 50% of his sentence (which will be 24 months).
It also means that he did not try to kill Michael.
I'm surprised that there are no stacked charges - meaning other charges that could make the Involuntary Manslaughter charge stronger. I'm disappointed, shocked and just really upset right now.