You're still entirely missing the point, so please allow me to clear it up for you. In the scenario we're discussing, specifically the utility of hidden containers with respect to plausible deniability, the police already have access to the outer container. Either the key decryption passphrase was directly conveyed to them, or they had the device owner unlock the outer container to facilitate spot inspection of the device and the device owner complied given his belief that he will be protected by hidden containers. At this point, the device is confiscated. If the outer passphrase was not supplied, it matters little at this point, because the volume is unlocked and mounted. The outer container key will be extracted shortly thereafter as a result by any one of numerous means.
The police now proceed to inspect the digital media in question. In many cases, said analysis will rapidly identify media regions which are likely to represent "hidden containers", and interesting interactions between the owner of the device and law enforcement personnel will commence shortly thereafter.
What part of this is unclear? Perhaps you should explain the nature of your experience with cryptography, preferably with emphasis on practical applications pertinent to this conversation.