I know you all think its micheal, but what if it was that russian dude, no one knows if he died, he put the grenade there and pushed himself away from the window, if he was meant to die, he woudnt chuck the grenade, seems quite probable that hes the one on the boat, also the people on the boat know everything about everyone on the island, so they woud recognise micheal, where they woudnt reckonise the russian guy.