the opening they thought could be a door to a 'fourth' chamber was apparently only the footprint a missing marble stanchion.
there is no apparent additional passage, so the third chamber could be the final one.
this is the room where they found the head and the fragments from the wings of the sphinxes, and the two (broken) massive marble doors.
this would make the third chamber the burial chamber, and in this case it would be obviously completely looted.
the excavations are not complete, and there could still be some sealed area, particularly under the floor of the third chamber. or so we ca hope
i find it very puzzling (and disappointing) that it would end here, without anything significant to mark the burial chamber (apart from broken pieces from the entrance).
it would also send my theory of the complex proceeding all the way to the geometrical center of the tumulus (
post #71) crumbling down
even if this is all there is, still a very exciting find, which will keep archeologists discussing who was buried there for ages.
http://archaeologynewsnetwork.blogspot.com/2014/10/amphipolis-dig-shows-no-doorway-to.html
... but I still hope they find a "secret passage"
here are some fragments of the wings
and a semi-official reconstruction of the entrance