Marseille prosecutor Brice Robin, citing information from the "black box" voice recorder, said the co-pilot was alone in the cockpit.
He intentionally started a descent while the pilot was locked out.
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.