>>64210394 (OP)
>>64210482
>>64210514
there will also be a lot of dna evidence of the victim. potentially in many places.
also the coroner will have an approximate distance and estimated height of the shooter based upon the direction of the shot travel and primary wound location. the closer the distance, the more accurate the estimate.
obviously there would also be reports from the neighbors of the approximate time they heard the shotgun being fired. yes, they heard the shotgun being fired. the sound from the shotgun does count as forensic evidence even if it's not that valuable.
any residual powder residue will make the shooters location fairly obvious at the time of the event, this does include if the shooter has distance. also the wad is rarely picked up when policing your brass but it most definitely counts as forensic evidence.
now that I think about it, I'm a little surprised nobody ever talks about putting identifying markers on the wad. without question it will be relatively intact. a custom or reloaded round would definitely have potential forensic evidence on the wad.