What it shouldn't be treated as, is an open and shut case. Skepticism given the circumstances, is in my opinion valuable here. There's very little to be lost from making absolutely sure that this wasn't foul play.
Sometimes murders are done as an open warning. The mafia has used that approach forever.
Why did the Russians use polonium to kill Alexander Litvinenko? Surely there were better ways to kill him that wouldn't leave behind a radiated dying body. Were they trying to make a statement? Seems plausible.
What could be better than to publicly kill the target in a manner that can't be provably traced back, but stands as an open and dramatic point for everybody else to 'learn' from?
Quoth the person who is apparently oblivious to the media shit-storm occurring right now.