From the ancient Greek philosophers of Socrates and Plato, the historical European philosophers of Kant and Locke, to modern psychologists of the likes of Marcus de Sautoy, there's always been a fascination with the human condition and identity. While we each conscious think of ourselves, and by transferability others, as autonomous individuals, there's always the presence of doubt; if our bodies and brains are really just a combination of complex cell systems, shouldn't our actions be merely a product of those systems given the outside stimuli we're exposed to?
This was tested when Sautoy, in the last ten minutes of his video, did a trial in which he was given two buttons, a left and right. It turns out that his brain patterns decided which button to push a full six seconds before he "consciously" pushed them. While this seems to suggest that the consciousness is merely an aftermath of the procedures of the brain, one could also conjecture that these kinds of things are imbedded in the processes of the consciousness, and the fact that one takes a while for that kind of thinking to surface doesn't deny the existence of his free choice. A personal theory is that the consciousness actually exists on a whole other spiritual level, and the fact that it mostly only interprets the speech production and interpretation parts of the brain is because those parts are most easily accessible and understandable.
However, I don't feel this kind of mystery can ever be solved. Just like most religions, most arguments for or against self-consciousness are based in a mystic, non-concrete realm.
Further, all the arguments any human being can make is based on our experience inside our consciousness, which itself falls to the illusion of the self. Whether it exists or not, we don't even have to perspective of to really understand what it really is. The main question in real question, then, may not actually be the definite existence of the free will, but how to refine the perception of us, our will, and our selves.