Towards the end of the story Summer of my German Soldier, what evidence leads the FBI to Patty?
Patty had bought a shirt for her father for Father's Day, and she had subsequently given it to Anton. Anton had been wearing it when he was shot and killed by authorities, and the shirt was traced back to Patty.
Patty had already almost been found out by the Sheriff. She had foolishly showed the ring Anton had given to her to Sister Parker at her father's store; although Patty had fabricated a story that she had gotten the ring from a tramp whom she had fed at their back door one day, her father overheard her and called the Sheriff. Patty told the same story to the Sheriff, and although the Sheriff was satisfied with what she said, her father was not.
A few days later, Mr. Bergen comes home early with Mr. Pierce from the FBI. Mr. Pierce had apparently questioned Mr. Bergen already about the shirt, but, having learned that Patty had bought it, had come to question her too. Patty tries to tell the FBI man the same story she has told Sister Bergen and the Sheriff, but she is no match for him under his insistent interrogation. When Mr. Pierce shows Patty the shirt, which has a hole and bloodstains on it, Patty breaks down and reveals that she had indeed been helping the escaped German prisoner, Anton (Chapter 16).