God knew but allowed it because we needed free will and what we use it on is of course of our OWN free will. Knowing what is going to happen does not make you responsible, especially (like with God) you give the person the chance and choice not to and if he does not take it then his fault. Knowing his answer is irrelevant, giving the choice is the important part and that is what God does.
Parva leves capuint animas but then again crazy stuff is so tempting