In chapter 8 of Avi's The Man Who Was Poe, Edgar Allan Poe, calling himself Mr. Dupin, doesn't necessarily meet anyone inside of the bank vault when he goes to investigate it, but he does meet someone important who escorts him to the vault. When Poe, calling himself Mr. Dupin and posing as insurance company investigator Mr. Grey, visits Providence Bank and asks to examine the vault from which the gold was stolen, Mr. Peterson escorts Poe; therefore, Poe meets Mr. Peterson while visiting the vault. Based on Mr. Peterson's appearance, Poe is able to figure out Mr. Peterson is working with Mr. Rachett as an accomplice in the murder of Mr. Rachett's wife, the kidnapping of Sis, and the gold theft.
Mr. Peterson is described as looking like the youngest clerk working at the bank and as having "hair so blond as to be almost white" (75). The nearly white hair is an important clue because, earlier in the story, on the foggy night Sis went missing, Edmund was approached by someone he thought was a "very old man," but his face was so covered by his scarf that all Edmund could see was the man's "eyes and white hair" (8). The white-haired man asked Edmund for help finding Shamrock Street, and Edmund escorted him, although Edmund knew doing so would keep him away from Sis longer than he should be. Poe quickly understands the white-haired man intentionally distracted Edmund while Mr. Rachett kidnapped Sis. If the white-haired man was really young Mr. Peterson of the bank, then Mr. Peterson and Mr. Rachett are most likely partners.