Free Will is the power of a conscious mind to have control over its environment, future, and "destiny".
Christianity and Free Will
If God knows what you are going to do in the future, then you really have no say in the matter. It doesn't matter what you do, you will always end up living the future that God already knows about.
Also, the doctrines of predestination, and that God is the Creator of all things, contradict the idea of free will. If God has a plan for us all, then no matter what you do, it's God's plan. That, presumably, includes killing, or raping somebody, or (gasp!) being an atheist.