I’m 100% convinced the car journey didn’t match their alibi- and possibly both cars were being used during the same period, or overlapped timings wise. (hence the joint enterprise, both have lied to create an alibi but in collaboration together) And this is the evidence (which probably isn’t enough in a trial), but enough to charge them. The other possibility is the mobile phone signals, but they only give rough areas. The police knew the car journey that night 100%, this is why they are searching at certain locations that seem quite spread out and random- I’m guessing the car stopped at these points. I suppose as someone pointed out there is a small chance (even though it seems completely unlikely) that BW is alive and hiding and her parents are innocent and we’re out looking for her that night. The trackers on Mercedes have been fitted as standard since at least 2009 (when we owned one)- they are a feature that allows you to alert the emergency services or breakdown by pressing a button on the dash, there cars were much newer models than that.
Edited to add: I know some have questioned that this might not have been available on their cars, but even if they didn’t use it, it did track etc and certainly existed 11 years ago (found a dated link rather than just a forum discussion about it)
Mercedes 'mbraces' Telematics