he can only pretend that someone stole his car

Not really. He drove it later that morning down to Albertsons and I believe they have him on camera getting out of his car there.

But if LE doesn't have any footage or images showing a back plate on the suspect vehicle (not necessarily legible), they could try to create doubt that it was his car at all. No front plates is only an indication that it's his car because he's from PA, but many people remove all plates or use fake plates when committing a crime. So maybe there were no front plates because the suspect vehicle had removed both plates, in which case it could have been any white Elantra years 2011 - 2016, and not necessarily one originally from out of state. Footage shows the vehicle driving to WSU and taking a path consistent with where BK lived, but there's no footage showing the vehicle parking, and that info on it's own would be too weak to convince most that it's 100% his car.

If they can create doubt that it's his car, then they would only have to contend with the DNA and phone records. The phone records are pretty dependent on the car being his, and the DNA will be difficult to explain away, but not impossible. That's a lot of "if's", and none of that sounds easy, but you see how, based only on what we know right now, they can start to create reasonable doubt.

It might not be enough doubt, and there could be more damning evidence on the way. This is all still so early.