[Sacajaweau]

Looks promising unless it says “Made in Japan”.

[hoosiermama]

Much smaller search area today!

[Robe]

The CVR only records 120 min of cockpit conversations then it starts recording over itself. The FDR recorder will record 25 hrs of flight data (28 different parameters I think).
So I don't think the CVR will be of much use, unless the crew was alive and talking til the end,or the deranged pilot was sitting there ranting and raving.
The FDR could prove interesting however, like when the cabin pressure was dumped, etc.
As for locking the copilot/cabin crew out of the cockpit, all I'll say is the crew have a way of getting in.
BTW the passenger oxy masks can be turned off/or deactivated from the cockpit, if there is a fire on board the aircraft, masks are not deployed, as the production of oxygen may further fuel the fire.