What clues does Lee give the reader about Ewell's death? What conclusion can the reader draw from these clues?

Ewell's death really isn't spelled out for us but it is safe to assume that Ewell was killed by Boo Radley. The smell of "stale whiskey" and Bob's knife, "metal ripped on metal,"were strong clues that Bob was stalking them.

... a shiny clean line stood out on the dull wire. "Bob Ewell meant business," Sheriff Tate muttered.

In the end it was clear that Boo was the kid's guardian angel.