A 15-year old Conway, New Hampshire girl who went missing October 9 has been in contact with her family.

Investigators say Abigail Hernandez wrote a letter to her mother on October 22, two weeks after her disappearance. It was postmarked the 23rd, but didn’t arrive until November 6.

FBI Special Agent Kieran Ramsey says officials have confirmed its authenticity.

"When we received this letter, I will tell you it was unprecedented we have not seen anything like that in recent time in other investigations, but most importantly it gave us hope," says Ramsey.

Police aren't releasing the letter or where it was postmarked. New Hampshire Associate Attorney General Jane Young says Hernandez may have left willingly, or could have been manipulated to do so.

"We are concerned for her safety," says Young. "She is not out there alone. She has somebody who is either helping her, whether that be a friend, or what we fear is a foe."

Young says she has "grave concerns" for Hernandez’s safety. She urges anyone with information to contact law enforcement.