Very good question, i suppose when a person reaches a certain social status and has a lot of influence.

Amount of influence. If you have ever managed to get a group of folks to do your bidding- then you're important enough to be 'assassinated'. Which is why Michael Jackson was considered to have been "assassinated".

A figure in the public Eye is usually assassinated by those who oppose & object their beliefs & popularity. When a public figure is making massive changes the few become disgruntled.

"Assassination is the targeted killing of a public figure. Assassinations may be prompted by ideological, political, or military reasons. Additionally, assassins may be motivated by financial gain, revenge, personal public recognition, or mental illness. The terms targeted killing/assassination may refer to the government-sanctioned killing of opponents[citation needed] or to legitimate attacks on high-profile enemy combatants." "The definition of "assassination" varies among sources. The American Heritage Dictionary defines "to assassinate" thus: ... to murder [a prominent person] by surprise attack, as for political reasons; however, the Oxford English Dictionary's definition is: The action of assassinating; the taking the life of any one by treacherous violence, esp. by a hired emissary, or one who has taken upon him to execute the deed. There is dispute whether the term assassination should include killings wherein the primary motivation is attracting attention to a political cause, and wherein the victim is of secondary importance (and might be famous, but unrelated to the dispute, or even an unknown). This leads to a number of possible definitions - which may however not all apply in any specific case: - the killing of someone by treacherous violence - the killing of someone in the public view (i.e. someone notable) - the killing of someone for political, moral, or ideological reasons For the purposes of this article, the third definition predominates, even though the second is often used, and the first would often be found in colloquial use." Source and further information: http://en.wikipedia.org/wiki/Assassination

Governor Long of Louisiana was murdered in the 1930's, and everything I've ever reade/seen/heard about the incident states that he was assassinated. My own opinion is that anyone holding an elected office and is murdered while serving is assassinated.

When it's a public official from Mayor, Congressperson, up to President and the act is premeditated or there's a political reason for it