They story was untrue. The plates were not stolen. The same media that reported this "fact" also reported the "fact" about them joking.
The plates were reported as not belonging to the car - making it a possiblity that the car was stolen.
They were traced back to someone in Chicago and it was verified later in the day that the plates were originally on another vehicle and there was a snafu in the plate transfer. The Police were NOT lying!!!
I also heard one of the law enforcement officials at one of the press briefings yesterday SAY that at least one of the plates did not match the vehicle. It was later explained exactly what vehicle it did match. It was never explained how the tag that clearly matched a specific vehicle ended up on that car. I think that overlooking this fact is part of some decision to let these people go. I think it is highly suspect that they suddenly "discovered" that they were wrong about the tag.