Weeks after she disappeared, missing New Hampshire teen Abigail Hernandez sent her mother a letter, authorities revealed Friday. “When we received this letter, I will tell you it was unprecedented,” said FBI special agent Keiran Ramsey. “It gave us hope.” Ramsey explained that investigators initially kept the letter a secret from the public when it was received on November 6, but made the announcement this week in the hopes that it might lead to her discovery. Investigators’ “worst fear,” Ramsey said, is that “someone may now be coercing” the 15-year-old. Hernandez has been missing since October 9, when she was last seen leaving her high school. It’s unclear whether she was abducted or ran away.