Help! (Don't read this if you have not finished the book)

I thoroughly enjoyed reading To Kill a Mockingbird, and it is a book worth reading twice. The suspense, sweet innocence of the children, and themes of family ties and racism kept me engaged. However, as I got near the end I was left with a question or two.

In chapter 30, Scout is retelling the attack of Mr. Ewell. By the end of her story, Atticus is convinced that Jem must have plunged the knife into Mr. Ewell, but Heck Tate insists that it was accidental suicide. I have my doubts as to whether or not Mr. Ewell fell on his own knife in the struggle, but I am not sure who was responsible for his death. I do not believe it could have been Jem, because at some point he was knocked out. Arthur (Boo) Radley was the one that rescued the children, so he had to be present at the end of the fight- was he the murderer? When Mr. Tate is telling Atticus that he wants to keep the incident quiet he begins describing what will happen if anyone finds out who ended Mr. Ewell's life.

"'All the ladies in Maycomb, includin' my wife'd be knocking on his door bringing angel food cakes...taking the one man who's done you and this town a great service an' draggin' him with his shy ways into the limelight- to me that's a sin'" (317).
The shy person Heck Tate is speaking of must be Boo Radley, right?
Who is the murderer, if there is one?
Let me know if you agree with me, or if there was something I am missing.
Thanks!