To kill a mockingbird what are the men at the jail house there to do

The man in the jail house tried to kill or find trouble for Tom Robinson. Luckily Atticus was there and Jem had the idea of following his father because he was worried. Scout later then solved the issue by mentioning Mr Cunningham's trail (or some sort I forgot) and they all realised that Atticus is just trying to do his job and justify the person like how he treats them. At last they went back and Tom wasn't harmed.