When Atticus first thinks that Jem was the one who killed Bob Ewell, what is Atticus ready to do? What does this show the reader about Atticus?

Atticus is ready to tell the truth. Atticus sees things in absolutes when it comes to the law. Sheriff Tate convinces Atticus that it is in nobody's interest to tell the complete truth when it comes to this particular case. Everybody will lose if the truth came out.