Since there was a train coming from the other side, the magician wouldn't have been able to watch his kill thus eliminating that platform as a place where the culprit is positioned and only leaving the conductor's seat. He could've saved a week's lifespan.
The dragon seems to be soul-linked to the witch so he probably won't confuse the two. They're probably chilling in the castle figuring out whether or not to raze the castle to the ground tbh
My bet's gonna be on her actually being the real daughter somehow and the "daughter" he found dead was actually a double or something. She looks too much like the both of them.