A Proposed Solution to the Problem of Free Will
The problem of free will has been generally argued on metaphysical grounds: If there is a God and man possesses a spirit, then man has free will. If man does not, and all things are matter, than consciousness is an epiphenomenon and free will does not exist. Of course, neither of these is really an acceptable option.
Leaving the question of consciousness aside for the moment, I think the confusion regarding free will can be solved by saying that it is a function of the mind: That to say that something was done by one's free will is to say that he would not engage in the action (or would do an action he would not otherwise do) in the presence of sufficient incentives and disincentives. If no regime of incentives could motivate the behavior or inhibit it, the action is not done by one's free will. If one can, the action is done by one's free will.
This may bother people. However, a person always does what that person's nature would have him do. If it is in that person's nature to kill others, it does not matter much whether his brain or his soul is corrupted. We know that subjecting the person to a penalty will reduce the number of murders---and that is all we need to justify doing so.