What clues did Atticus ignore that could have prevented Bob's attack on the children?

After the trial, many clues hinted Bob's intention of harm to Atticus and his children. For instance, Bob threatened to harm Atticus.

Explanation:

Bob Ewell was a poor white who was disgraced not only in the society but his immediate family as well. After seeing his daughter, Mayella, and Tom Robinson kis-sing each other, he persuaded his daughter to accuse Tom of mole-station and ra-pe. The case, though came out to be in favor of Bob, he was disgraced when he revealed the truth.

Bob spit on the face of Atticus, the lawyer of Tom Robinson, and threatened to kill him. Atticus ignored this clue, even after being a lawyer. If he would have taken that threat seriously, he would have been able to prevent Bob's attack on his children by taking precautions.