He didn't swim (walk; swimming ain't possible) from East Mitchell down the shoreline or across the Intracoastal, or at least not before it got dark last night. That particular route of escape was covered, by land and by sea.
If he swam from East Mitchell across to Jolly Bay, someone on the bay fill would have seen him.
General feeling is that he had someone he could call, and he got a ride out. There are several forestry trails one can take from EPW to 98 without being seen from Bay Drive or 395, and I don't know if anyone was stationed there. BUT, it's best not to take chances. He is already wanted for so much, another murder charge wouldn't worry him in the least.