You have to consider how much time went by before the computers, etc, were seized. Plenty of time for a computer whiz to remove many things. It just depends on how good the computer whiz is at cleaning up a pc.
Something tells me that this was is a "local" island thing that had not reach the internet yet. Someone was padding the pockets of these boys for videos of what they were doing to these girls. This is the reason why so many feet dragged on this case from the very start. I bet there are some high ups on the island that were enjoying these "private" homemade videos. The truth is now coming out as someone has found some of the victims and convinced and assured them that they will be safe if they come forward.