What evidence do you want/expect to see? Genuinely intrigued as so what burden of proof is deemed necessary in this situation.
Part of me thinks that if this was a made up charge to get him to the USA, they would want to ensure they had solid evidence to prosecute.
But to bring a prosecution the English prosecutors use a "balance of probabilities" test. As a random member of the public I want to know that the evidence they have is at least balance of probabilities before they bring a prosecution. The higher burden of proof is for the people at court to test. It's not for me to test the evidence against that higher burden of proof.
Sorry, I'm wrong, just thought of the other land border - Gibraltar and Spain. Still, he's going to do well to sneak across either of those... and sneaking around Europe, into Gibraltar, only then to sneak across the amazingly heavily guarded border there... is probably the worst escape plan I could think of.
Further edit: OK, Cyprus and Akrotiri, too, which is even further afield.