Picture this: You decide to move your hand, then you move your hand. An observer using fMRI or somesuch notes that they observe neural activity before you report making the decision, and they can even predict where and how you are going to move from observations of neural behavior.
If you are a materialist, how is this surprising? Of course neural activity precedes you being conscious of making a decision and taking an action---that is the mechanism by which you make a decision and take the action. What does it have to do with free will? Not very much, if anything. It only becomes a problem if you are a dualist and believe any conscious, free-will-iferous activity must come from an a-material, imperceptible "soul".