How does Paul die in A River Runs Through It?

Unfortunately, readers do not get direct narration that tells us about Paul's death. We find out about his death the exact same way that other characters get told about the death in the book's closing section. The last time that Norman and readers get to see Paul is when he and Norman are packing up their fishing gear, and Paul states again that he needs another three years before he will be able to think like a fish.
The book then jumps to May. A police officer arrives to tell Norman that Paul is dead. He was beaten, and his body was dumped in an alley. We are also told that nearly all of the bones in Paul's right hand were broken​. That seems to indicate that Paul fought​ back quite fiercely.