How important does a person have to be before they are considered assassinated instead of just murdered?

Answer 1

According to dictionary, an assassination would be a murder for political reasons, while a murder does not. Therefore, it is not how important the person is, but is it for political reasons.

Answer 2

It is not a matter of importance of the person, but the reason for the killing. John Lennon was important, but his killing was murder. You never heard of the federal judge in Austin that was killed, but the reason for the killing was the belief of the shooter that his version of government was better and more valid than the USA. Sometimes people will claim what they are doing is an assassination when most people consider it murder as in bombing an occupied church or shooting a doctor who does abortions. "They threatened our society, made war on it, so we killed them."
Usually murder includes a personal element or is involved in a crime, while assassination targets a person who has no relation to the shooter other than their public position.