Although cover-ups are common to many less-than-honest law enforcement officers, it doesn't come natural to Heck Tate, the congenial but businesslike sheriff of Harper Lee's novel, To Kill a Mockingbird. Although the reader may be left questioning who really killed Bob Ewell--Jem or Boo--it is actually the narration by the still innocent Scout that leaves the reader in doubt. Sheriff Tate is aware that only Boo Radley would have had the strength (and the weapon) to kill Ewell, and he will consider no other possibility. Atticus seems less certain than Tate:
"You heard what Scout said, there's no doubt about it. She said Jem got up and yanked him off her--he probably got hold of Ewell's knife somehow in the dark..."
But this is in part due to Scout's narration. She misunderstand's Atticus's argument and willingness to allow Jem to take the fall for Boo in order to avoid a public trial. Atticus is thinking like an attorney when he considers that Jem would be able to deal with the traumas of a trial better than Boo.
"... I guess the thing to do--good Lord, I'm losing my memory... Jem's not quite thirteen... no, he's already thirteen--I can't remember. Anyway, it'll come before county court."
It is in part because Boo has saved his children's lives, and Atticus would rather put Jem through the stress of a murder charge (albeit in self-defense) than force Boo into this predicament. But it is in Atticus's sympathetic character make-up to always put the other man first--even ahead of his own family.
Both Atticus and Heck are protecting Boo Radley from the horrors that he will suffer from a public trial. Even Heck will not allow this possibility--not over the death of someone as deserving of such a fate as Bob Ewell.
"God damn it, I'm not thinking of Jem!"
"... draggin him with his shy ways into the limelight--to me, that's a sin. It's a sin and I'm not about to have it on my head. If it was any other man, it'd be different. But not this man, Mr. Finch."