You can explore the Jenna route, where you'll find out what Leo actually saw. Of course, in the later stages of both Leo's and Flynn's routes, you'll also get some hints. Although Leo may appear a bit crazy in his own route, to some extent, he isn't insane; he simply noticed things that others overlooked. You can go back and revisit those seemingly nonsensical scenes in the later part of his route. In Jenna's route, everyone will discover a fact that should have been very noticeable.