Solution
The Hotel Hideout
Mr Ascher claimed some members of the Coffee Cartel were hiding out at his hotel. He said he knew because he saw them through the keyhole and recognised them.
However the flat key that Mr Ascher handed over to the Detectives was from a cylinder lock, the type which doesn’t have a keyhole you can peer through, and therefore Field Marshal Mogau knew it was impossible for Mr Ascher’s story to have been true!