Why does Atticus sit outside Tom Robinson's jail cell?

Atticus went to go stay outside the jail that night because he was Tom Robinson's lawyer. Tom Robinson was staying in the jail the night before the trial, and Atticus wanted to make sure he was safe. Scout and Jem notice there father has suspiciously left the house that night so they follow him to the jail. A mob of white, unfamiliar men come to the jail and tell Atticus to move away from the jail house door. He refuses. (These men were most likely a lynch mob, Klu Kux Klan) Right then Scout jumos out and tell the men to leave her father alone. She notices Walter Cunningham in the crowd, and she go's up to him and tells Mr. Cunningham to tell his song that she said hi. Because of Scouts dissruptance, the mob leaves and Atticus and TOm ROobinson were saved. Hope this helped