Maybe it's like a push poll.
I've come to the conclusion that the tip line is not much more than a public relations gimmick; its purpose is to allow the cops to say: "We're allowing the public to contribute."
It's similar to when government conducts a public meeting or a public hearing on an issue. The officials already know what they're going to do in 95% of the cases; but, by allowing public input [see "Environmental Impact Statement" - :>)], they fulfill the legal requirement for public involvement. In most cases, the officials consider such public input as being "something that's gotta be done", but they don't really endorse the practice - they merely give it lip service.
Even in this case, I saw the license number on FoxNews channel first, continuously toggling between them and MSNBC and CNN. And now I find out that the police hadn't wanted the license number released; yet, it was the public, not the police, who first found the vehicle. And here's the question that keeps coming back to me: "Why hadn't the police been cruising through obvious places - parking lots of shopping centers, WalMarts, and rest areas - looking for the suspect vehicle? That would have been my first place to look! It appears to be so easy to hide in those places, or get rid of unwanted items in public trashcans at those locations!