(CNN) -- Federal and state authorities won't say specifically why, but they think a letter purported to be from a New Hampshire teenager missing for nearly two months might in fact be the real thing. 

Abigail Hernandez was last seen on October 9, according to the FBI, as she headed home from her high school in the town of Conway, and officials fear she might be held against her will. 

"We are concerned for her safety," New Hampshire Associate Attorney General Jane Young said Friday at a news conference called to discuss the search for the girl. 

"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." 

At the news conference, authorities revealed that Abigail's mother, Zenya Hernandez, received a letter on November 6 that appeared to be from her missing daughter. That letter was kept secret until Friday, said Young, because "law enforcement had to take every possible step to verify its authenticity. 

"And at this juncture, we believe in fact that it was written by Abby and was sent to her mother," Young added. 

Neither federal nor state authorities would discuss the contents of the letter beyond Young saying the writing is in "a tone Abby would have used," and that the letter underwent "expert analysis" before its existence was announced publicly. 

Officials also said revealing details about the letter could potentially trigger "copycat" letters that would slow down the investigation. 

The letter was written on October 22, and postmarked on October 23, according to Young, and it was turned over to authorities for investigation after Zenya Hernandez received it nearly two weeks after it was postmarked. 
Who is this story about?
When was she last seen?
Where?
Where was she coming from?
In what State?
What was received on November 6?
By whom?
Who received it?
What's her name?
Why was the letter not made known immediately?
Which authorities were investigating?
When was the correspondence written?
Was it mailed or hand delivered?
Did it have a postmark?
On what date?
How long afterwards did mom receive it?
Abigail Hernandez
Abigail Hernandez
October 9
Abigail Hernandez was last seen on October 9
Conway
Abigail Hernandez was last seen on October 9, according to the FBI, as she headed home from her high school in the town of Conway
high school
 from her high school 
New Hampshire
a New Hampshire teenager 
a letter
received a letter on November 6
Abby
"And at this juncture, we believe in fact that it was written by Abby and was sent to her mother," Young added.
her mother
 authorities revealed that Abigail's mother, Zenya Hernandez, received a letter
Zenya Hernandez
Abigail's mother, Zenya Hernandez
to verify its authenticity
 That letter was kept secret until Friday, said Young, because "law enforcement had to take every possible step to verify its authenticity.
Federal and state
 Federal and state authoritie
October 22
The letter was written on October 22
mailed
postmarked 
yes
postmarked on October 23
October 23
postmarked on October 23
nearly two weeks after
nearly two weeks after it was postmarked.