This is a specific usage, in its original context and native habitat, of what is technically called the Hot News sense of the English Perfect construction. There are four senses in all (cf. McCawley 1971):
(a) The Universal sense of the Perfect, used to indicate that a state of affairs prevailed throughout some interval stretching from the past into the present
- I've known Max since 1960.
(b) The Existential sense of the Perfect, used to indicate the existence of past events
- I have read Principia Mathematica five times.
(c) The Stative/Resultative sense of the Perfect, used to indicate that the direct effect of a past event still continues
- I can't come to your party tonight - I've caught the flu.
(d) The Hot News sense of the Perfect, used to report hot news
- Malcolm X has just been assassinated.