Solomon Northup's Narrative

I read the beginning of Solomon Northup’s Narrative:  12 Years a Slave, and I learned in detail about how Solomon got kidnapped and taken away. He gave a lot of detail explaining his family's background and how he is a free black man. He talks about how he knows now that the people who took him are guilty, but he had no idea back then. Were his kidnappers just very good at lying? Did they take him just for the money? Why didn't he write a letter to his wife about where he was going?