I'm certain that there have been isolated loonies who murdered people in the name of Satan. That said, having studied the history of witchcraft and the occult (at a major public university, no less), I'm aware of no organized (i.e. larger than two or three loonies) groups that murdered people for Satanic reasons in modern history. But that's probably because a) any large groups usually have at least one member break and tell the police, which hasn't evidently happened and b) the most efficient groups have obviously not been uncovered yet.
