Semantics -- Anyone that is murdered not in the heat of passion...if it was premeditated -- is an assassination. Anyone that murders a political figure, celebrity, etc... has likely been planning it and is therefore definitely an assassination.
Assassinate 1. to kill suddenly or secretively, esp. a politically prominent person; murder premeditatedly and treacherously. 2. to destroy or harm treacherously and viciously: to assassinate a person's character.