Like where you can see teddy graham people, human fire hydrant, human kite, haunted synagogue, etc.
Hose it down to clean it up. As long as the gas nossels are clean it should be fine I would think.
They don't really know who did it, but since they were standing in front of the Radley home Jem automatically assumed that it was Boo Radley since his brother Nathan was helping with the fire. The book does not come out and directly state it though, its just Jem's theory.
