How does Leper give away his secrets to Finny and what happens?

In Chapter Eleven, Brinker, who is far more obsessed with Finny's accident than either Gene or Finny are, is holding some kind of inquiry into the accident, with a few other boys there to act as an examining jury. Brinker brings Leper, who was at the scene of the accident, out to speak; when Leper says that Gene did indeed push Finny, Finny freaks out and runs from the room. He falls on the marble steps outside, and re-breaks his leg.