How did Heck Tate alter the evidence about Boo Radley killing Bob to fit his lie?

The other teacher is correct. In chapter 30, Heck Tate and
Atticus are discussing what happened and Atticus thinks at first that Jem was the one
that killed Bob Ewell. Heck insists on calling the death an accident, but Atticus, ever
the fair and impartial lawyer, doesn’t want Jem protected from the law. Heck insists
that Ewell fell on his knife and that Jem didn’t kill him. Heck knows that Boo is the
one who stabbed Ewell but he wants to keep the facts secret. He says that Boo, with his
"quiet ways", doesn’t need the entire town bothering him any more than they have in the
past. He reminds Atticus that Tom Robinson died for no reason and now the man
responsible for that miscarriage of justice (Bob Ewell) is dead. “Let the dead bury the
dead,” he tells Atticus.

Some of my students have taken
issue with this ending - the fact that Atticus agreed to keep things quiet. They said it
was out of character - that a man who was even willing to allow his own son to be
exposed to the workings of the law (when Atticus thought it was Jem who killed Ewell)
would not have so easily agreed to hush up Boo's deed. What do you think about this? I
think Atticus did act according to character because sometimes we
must listen to a higher power, and surely that power would not have wanted Boo to suffer
any further abuse.