I think LE was onto Moody as a POI earlier than the public was made aware. Possibly in the first few days.
LE was not obligated to tell the public if they had video of Brittanee getting into a car. They don’t always release all they know for many reasons. My guess would be they didn’t need help identifying the car. Maybe they tracked the car owner down pretty quick which led them to Moody. I bet we will find out he was questioned early on. Richardson said this all came together from a lot of different ways including an informant. I don’t know if he is referring to this girlfriend or not.
None of this makes sense though with the FBI being adamant about the story involving the Taylors just 5 years ago. If they knew the car had some link to Moody, I can't believe they'd fall for the informant story. I wonder how the quality of the video was? I can't think it was that great because it has taken 13 years to find Brittanee.