He is a murder in the same sense that the Roman clergy at civil trials were murderers for the inquisition.
==With one swipe you have thrown aside all of the historical facts in favor of an anti-John Calvin opinion. As I have said, Calvin had no say in the fate of Servetus. The proof of this is his request to change the method of execution. His request was not carried out. If you want to blame someone for the death of Servetus blame the little council of Geneva and Michael Servetus. While I don't believe we should execute heretics, I do believe Servetus was a heretic who has most likely burned twice (if you get my drift). If he had stuck to medicine and stayed out of Geneva or repented of his sinful statements he would not have been executed (via any method).
I'm not defending the Roman clergy in this but to use the same argument in favor of Catholic Clergy who did not kill the heretics themselves but accused them and approved them for death by the civil authorities is no greater an offence than Calvin doing the same thing. Though you do suggest and I agree he was wrong for complicity.
==First, there was very little separation of church/state then as there is today. Often civil/church authorities were the same or closely connected. That is one reason why they believed it was right to execute heretics. They, protestant and Catholic, believed the government should use the sword against those who do wrong in every area including theology. While I don't believe that is a correct understanding of Romans 13, I would not go so far as to accuse any one person of murder simply because they agreed with the system (generally or specifically).
Second, while Calvin (as far as we know) had no problem with the execution of Servetus, the matter of his execution was not in Calvin's hands. Calvin was right to call the heretic down on his heresies. However, as I have already said, I think he should have stayed clear of the trial. If for no other reason he should have stayed clear because he gave those who disagree with him a wonderful red herring argument to use whenever they want to argue against Calvinism without dealing with the points of doctrine. I've seen it done time and time again mainly with the issue of eternal security.
Third, Calvin was certainly morally and theologically wrong for his complicity in the execution of Servetus. However I don't believe he can rightly be charged with murder. Poor judgment, yes. Poor theology (on this point), you bet. Having a big blind spot, certainly. However the murder charge seems to be rather extreme.