I agree with you. We always get the doubters in every case, the ones who believe that because LE doesn't keep us informed, they aren't any closer to solving it. No matter how many times they're reminded, some still just can't grasp the fact that LE does not have to release any information about a case while it's being investigated. Even though the media always screams that the public has a right to know, that is not true. We do NOT have the right to know anything, unless we're local and it concerns our safety. Once they find and arrest whoever took Sierra, I'm sure more details will emerge.
If they thought they had a serial kidnapper/murderer on the loose, you bet, they would inform the public of certain things and warn them to be vigilant. But obviously, they don't believe this is the case, so keeping it close to their vest is in LE's best interests. The less the public knows, the better their chances of catching the perp and solving the case. Ask any LEO with investigative experience, they'll tell you the same thing.
I've often wondered, what would happen if we did know everything they did? What would we do with that information? NOTHING, except sit here and talk about it.