Players don't kill people, state based actions do.

The situation you are describing is one where state based actions kill someone in the draw step, which is temporaly removed from when they got milled, but is essentially no different from being lightning-bolted to death: sure, there is a player who put him at 0 life, but the state based action killed him. Following this logic, there is never someone who killed another player.

I am in favor of the ‘let the dead player decide’ method.