Ballistics probably won't tell much, per se, but wound channel angle might, powder burns (if present), location of the bullet either inside or outside of the body (if recovered and if a through and through wound with little or no deflection off of skeletal elements).
Blood and tissue distribution in the grass/on the sidewalk, etc. from an exit wound could provide the location at the time of the shooting, and to some degree the angle of the shot. (Warm climate, wait a day and watch for flies--they'll locate the meaty bits.)
Anyway, Levin's world, and life is on the line here. He's going to figure if he stays out of prison, he can relocate and work to pay the bills, whatever they are.
I have to believe that the prosecutor selected charges which have some likelyhood of producing a conviction or which they deem appropriate to the offense. Mitigating circumstances might include an unrelated death threat or other factors we will not read about in the papers. Keep in mind that most newspapers are owned by media outlets which are anti-gun and which are perfectly willing to hang any CCW permit holder (even though he probably didn't need a permit in his home), just to further the 'Dodge City' myth.