Announcement overnight by the Malaysian PM: they can now state definitively that Flight MH370 ended in the southern Indian Ocean & there are no survivors.

As far as I can tell, this comes after advanced data modeling was done on the satellite data. I'm not sure how they reached the conclusion that there were no survivors, except that they must have had a number of scenarios mapped out & this one fits a picture of the plane &/- pilots being incapacitated & therefore the plane flying until it ran out of fuel (presuming that the pilots would otherwise have initiated some kind of emergency landing).