I think that the freedom of the will, like everything, is relative. Relative to physical barriers, everybody's will is free in the absence of them. Relative to other people, our will is free so long as they do not force our hand. Relative to experience, our will is less free and more bound to the events and encounters that shape our worldview. Relative to our mind, our will is, again, less free and more bound to the inclinations and limits that it sets for us.
In short, I don't think that our will is entirely free or entirely bound to any one thing. I think it's a bit more complex than that. When we're acting, it often feels as if our actions are entirely within our control, but then if will look back on our experiences or examine the mental state we're in, we're often confronted with the reality that we had less control than we thought we did. After all, if I touch a fire and get burned, I'm not going to touch fire again and even though I choose not to touch fire again, that choice was, in great part, determined by my previous experience with fire, by my mind's ability to remember that experience, by my mind's ability to apply that memory to the present reality and so on.
This is why I have trouble getting angry at the killers. I don't perceive events like this as simply as "he's evil and he chose to do this". There's always more to the story. Choice is not the final story. We choose things for reasons. There are causes for our actions - good and bad. And yes, I know, there are plenty of people with mental disorders and illnesses, with bad childhoods and so on who don't shoot up schools. But those people don't erase the realities that influence the will (or choices) of killers and other violent people I'm talking about.