One who murders by surprise attack.... sniper?
How about ASSASSINS?
Interesting word derivation for assassin...
Word History: At first glance, one would be hard-pressed to find a link between pleasure and the acts of assassins. Such was not the case, however, with those who gave us the word assassin. They were members of a secret Islamic order originating in the 11th century who believed it was a religious duty to harass and murder their enemies. The most important members of the order were those who actually did the killing. Having been promised paradise in return for dying in action, the killers, it is said, were made to yearn for paradise by being given a life of pleasure that included the use of hashish. From this came the name for the secret order as a whole, an, “hashish users.” After passing through French or Italian, the word came into English and is recorded in 1603 with reference to the Muslim Assassins.
Definition courtesy of Dictionary.com
