To truly understand "free will" you must understand some basic truths.
Sin, in anything outside the expressed will of God.
Evil, is malicious intent to commit sin.
And "Free will" is simply your ability to choose something not in God's expressed will for you..
Or in other words when you exercise "free will" you sin. Because if in fact you were in God's expressed will then you'd be "In God's Will" and not your own. (Kinda like your zombies)The fact that you do things outside of the expressed will of God should prove that you in fact have a will of your own.
Also he would have had to create the tree of good and evil and would have created Satan. So freewill is based around what God put in the humans head.
As the previous poster mentioned, Even though "we" may program a computer with parameters and limitations, what makes AI, AI is what the processors do with what they have been Given.. The Same is true here. God did place the tree in the garden, because without a true choice. Either, God's expressed will, or that of our own. (represented by the tree) Their can't be free will. The whole point and purpose of this life is so that we may prove to ourselves in whom we will choose to live. God wants us to choose Him. But with out options then their can't be a choice..
This is what happened to satan and his angels.. They weren't given the chance to prove to themselves in whom they would live for, or they weren't given an equivalent of this life, and so they were all just placed in the presents of God.. A great number of whom did not want to be there, so
they risked Literal Hell for a chance to escape God, and yet hold on to creation... So yes in a sense God did create Satan, but he is not the great ruler of the underworld stories have made him out to be. He represents rebellion, and a desire to live for one's self.. None of these qualities need to be forced on any of us. We want these things for ourselves. Which again is a product of free will..
Kinda like the whole Atheist movement. If you (Or others like you) were under God's will then your actions or thoughts would not be possible, but the fact that you can exercise your own will over that of God's expressed will for your life, shows that you in fact are choosing these actions for yourself...