I have a hard time believing the US authorities want anyone to detain Snowden besides US authorities. He is, presumably, sitting on a big pile of classified but as-yet-unreleased information. Pure speculation (what fun!): perhaps Hong Kong law enforcement and the US know precisely where he is, but they are biding their time until they can get their ducks in a row for a US team to bring him back. All these public statements are just for show.