The minute-by-minute account of the last half hour is interesting. One can construct a few, not-too-compelling alternate interpretations. The deliberate actions of a co-pilot seems most convincing. If they find anything remaining of the co-pilot's body, they might be able to determine if he had a seizure of some sort, but yes, the recorder said so-pilot was breathing normally. MESSAGE TO AIRLINES: Pilot should always have alternate means of getting into cockpit if the door seems locked from within.
They do have an alternative - to an extent. This video and this article explain it, but there is a procedure that can be followed that allows a person access to the cockpit. However, that can be manually overridden by whoever is in the cockpit at the time so we can only assume that the co-pilot denied the pilot access to the cockpit.