I said this in another thread: It's a no brainer that Hannah got into that car probably willingly with JM. No surprise about that. They probably can prove she was in that car with some forensic evidence, DNA. They might even be able to prove she had sex with JM in that car, though I doubt it given his size. Doesn't particularly matter. No crime giving a girl a ride in the car, any more than picking her up at the mall.
Given that LE got a search warrent for that car, I'd say they somehow were sure that Hannah got into it. That they seized it for evidence makes me thing they did find some sign of her. That they still couldn't touch JM with all of that makes me believe that it doesn't matter what they found. No proof that she was killed, or harmed. I don't even know if that "assault with the intention to defile" would stand up in court without some pretty good forensic evidence. DA was very reluctant to press any charges against JM, Long made that clear.
Though common sense, and probabilities tell all of us that something bad happened to Hannah after whe left with JM and that JM probably was responsible, it has to be proven. It takes more than a hair from her head in that car, on JM's clothes to prove that. So what if she went in the car, so what if she had sex with JM? It's what happened in terms of crime, was she harmed, killed, and proof of that, which is needed. It's really important to find Hannah' s body, because without it, or without some other strong DNA evidence as the state did have on RAT in the AM case, getting a conviction in this case on JM, even getting the DA to take it court is up in the air.
So whether there is tape of Hanah getting into the car or not, doesn't matter. It's a foregone conclusion, likely provable that she did go into that car, and with JM. That part is not a crime.