Ch6, Key for prisoner is not where bloodb's guide shows (this time through playing)

[Bloodbuster]

The keys will not appear until the cut-scene has played out.

You'll see this in Mole Temple. If the key does not drop by the beast you have to kill before unlocking the laser-door, they will be in the rubble. But, they will not appear until after you have approached the lasers and been told that you need to find a key.