That didn't answer many of the questions, but thats ok! I get that you're busy, and don't want to ruin the story for us!

I'm just gonna keep asking questions in a different direction instead. This time, not dealing with how the platinum society treats death, but how death interacts with Pokemon!

In the Pokemon universe, it seems there are a few pokemon that deal with the souls of the dead- specifically in this case;
--- Phantump, who in some entries is "the soul of a child who died in the forest". Could we see William come back as one of these?
--- Pumpkaboo, whose description is like "The spirit residing in the pumpkin is trapped in this world. Pumpkaboo can carry wandering spirits to where they belong, so they can move on." Which could be a really cool way to show that Williams spirit is trapped in this world!
--- Lampent, who senses when someone is about to die (and is most often found in forests) and steals the spirit. Could this death make one of these appear?
--- Duskull, which "lives in forests and enjoys the crying of children" is also a possible contender, since many of the team are in tears, right? Maybe?

I totally understand you can't tell us about plot things, but do these pokemon exist in platinum, and could death influence them? Could this murder (totally unplanned, but certainly a choice that was made by the players) influence a pokemon we encounter?

If theres anything more you can tell about the procedures surrounding death in that Pokemon world, I'd love to hear them!