From an absolute perspective, free will is untenable, because, among other reasons, it implies that each person's will is a separate axiom of the universe - which would violate Occam's Razor.

From a legal perspective though, we can consider someone to have acted with "free" will based on how predictably their choices proceed from what we know about their circumstances.

For instance, if someone had a gun to their head, and proceeded to follow the orders of the person holding the gun, we would say those choices weren't free - because we can reliably predict that they would obey the person with the gun.

Of course they theoretically have some choice not to obey the person with the gun. But the place where we draw the line is with what we ourselves would hope to be forgiven for if someone had a gun to our head.