I have a shop; our CCTV system is fairly new and it auto-wipes every seven days. I don't think this is unusual. I believe the police recommend 30 days or so as a maximum. As an aside, our time stamp is often wrong due to short power outages/accidentally turning off camera etc.
Re the legs sticking up in the car; could it be possible that Leah got willingly into a car, knowing that she was not going to be returning home and that, as they reached the busy junction the driver told her to slide down and hide in case anyone saw her and the driver was assisting this? As another aside; I don't think it's that weird to see someone with their legs sticking up like this. We were told off by the police once when I was a lot younger because I was sitting slumped back in the passenger seat with my feet up on the dashboard while waiting in idling traffic. Yes, I know - it was stupid!
In response to DeadStick; no, I don't think the crying girl was Leah. The girl seen was on the phone and we know that Leah's phone had been turned off by that point. Some people have suggested Leah could have had a second phone but if this had been the case why would she have turned off her other phone the night before?