Sam Harris has a lot to say about free will (some of them are worth a watch) but he raises some interesting points. When I think about free will, I think about the process of a thought. An idea, the compelling urge to do... something. In order for us to be the true 'authors' of our actions, whatever they might be, we would be required to know what we were thinking before we thought it. I don't know the exact structure of my next sentence any more than you do. Does that mean that we're not responsible for our actions? No... obviously we have some level of control before instinct kicks in. It's something I had to think about for a while... we the things I'm thinking are actually coming from and how completely powerless I am to either stop or change them.
That whole concept brings us to another interesting point. If we think of... say... a serial killer. When he's caught, he's probably going to spend the rest of his natural life in jail. Rightly so, morality would dictate. Now... if we fully understood the neurophysiology of any murderer or serial killer's brain, if we could somehow see how the genome combined with entanglement with other people, events and experiences helped sculpt the micro-structure in their brain so that it was guaranteed to produce violent states of mind ... I'd submit that it could be considered as exculpatory as finding a personality-changing tumour which we could attribute to the actions of the murderer.
These kinds of observations make me think that free will is an illusion.