The German Minister of the Internal Affairs says that "it was clear that he was Islamophobic" for the Saudi, the terrorist from Magdeburg. Everything is of course possible, maybe he is just a notorious madman, but I would say that actions speak louder than words. Especially in a person with a medical degree who possesses intelligence and the ability to mimic.
I'm not Sherlock Holmes, but in looking for the killer's motives, I would consider the mass trampling of people at the Christmas market more important than his social media posts.
And then we are surprised that citizens do not trust institutions and that right and left extremism is growing.