The train still has to arrive. If it stops for some reason, the person won't die. Ultimately it wouldn't lay in your hands. Of course, if the trains comes, you would be responsible for the death nonetheless.

The same applies to a scenario, where Graendal used Slayer as a tool to kill Asmo. She would be responsible of course, and thus be "an indirect offender". But the question was always who stood there, when Asmo entered the room and pulled the trigger, so to speak. Makes vastly more sense that Slayer did that job.