I agree. The flight data recorder will show if the pilot set the plane to descend or not, how he input it will be the key to solving the mystery I think.
descent profile looks like autopilot... probably just input a descent rate on the Mode Control Panel (MCP) or whatever its called in Airbusese.
Now the curious factor is the statement made today by the authorities
"He said Lubitz had never been flagged as a terrorist and would not give details on his religion or ethnic background."
The part about "not being flagged as a terrorist..." create speculation that that is precicesly what the authorities are considering right now. Those facts will certainly be revealed shortly so why the secrecy?