This is an interesting question. It is clear that Atticus and Heck Tate are old friends, though possibly not intimately, since the sheriff is aware of Atticus's old nickname--"Ol' One Shot"--and his reputation as a marksman. Heck may have been the sheriff, but he "almost threw the rifle at Atticus" when it came time to dispose of Tim Johnson. Heck comes to visit Atticus just before the trial to warn him about possible trouble at the jail, and Atticus treats him with kid gloves during his testimony during the trial of Tom Robinson. In the final chapters, Heck trusts Atticus enough to share the truth with him: that the sheriff will deliberately falsify the facts of Bob Ewell's death, claiming that "Bob Ewell fell on his knife" rather than involve Boo (and Jem and Scout) in the investigation. Interestingly, Atticus always refers to Tate as "Heck" (except when he calls him "Sheriff" in the courtroom), while Tate always addresses Atticus with the less familiar but more respectful title of "Mr. Finch."