I don't think that question is more interesting or important because I don't think it makes a tangible inquiry. A universe with free will looks exactly the same as one without. What do we care about when we ask "are we truly responsible for our actions?" What is the distinction between true responsibility and deterministic responsibility? Whether you freely decided to reply to my comment or were determined to do so based on an unbroken chain of physical events since the beginning of the universe, the logic behind your locomotion remains the same, a decision was calculated based on data stored in your physical/non-corporeal brain; if you had a choice, you would have done the same thing, if you didn't have a choice, you would have done the same thing.
If we have no free will, then a human killer is as much to 'blame' for killing as the crocodile is.
To me, the idea that moral culpability might hinge on the true nature of free will seems flawed since morality is a construct defined within the scope of physical consequences that arise from human behavior.
We ascribe moral culpability to the human killer not because of their choice to kill, but because of our own perception that the killer understands what it means to take another life. You might say "more precisely, because of their choice to kill within the context of that understanding", but human morality is not equipped to consider the absolute nature of our choices. Be it a truly free decision or a determined one, the human killer's programming matches our description of morally wrong i.e. "understands what it means to take an innocent life, but does so anyway".