I really think LE can probably account for BL up until Sept. 11th. The "eyes on him" is video footage from stores, cctv, neighbor sightings, whatever. But, suddenly, GP's mother starts texting the L family on Sept. 10th, warning them she is contacting law enforcement, and BAM, BL is never seen again.
I kind of wonder if BL just quietly waited once he got back to FL to see what was going to happen before bailing. The dumbest thing he did was drive that van home, though. It's a decision that suggests, imo, that he reacted quickly and without much forethought. However, he could have said, "yeah, mom and dad, we decided to take a break so she said she'd fly home..." (or whatever). He had to figure that eventually her family would come looking, likely contact police, and sooner or later he'd have to come up with something. But I bet he never imagined the world-wide attention this case would receive, or that his face would be plastered all over the internet. He probably hoped she'd never be found and nobody would even know where to look (he didn't know the van was on private video).
Maybe it's possible he took off early on 9/11. His parents knew something was up (if he hadn't already told them when GP's parents started calling) so they got their lawyer involved and by that night, when LE came knocking, they were prepared with his card.
For locals, how strict are they about parking at Myakkahatchee? If he parked a car in the lot on a Friday, would it get ticketed over the weekend? The ticket was placed on Monday. The date his parents last saw him has already changed once, so I'm not necessarily relying on that.
