The question of why would "she" deliver the letter to the news paper instead of the police is IMO a significant piece to this new puzzle.
IMO in a normal investigation this would seem like a publicity stunt to me, but, this is not a normal investigation and it would appear that someone wants the truth revealed and believes LE is not doing that. Interesting that LE wants this informant bad enough to collect fingerprint evidence from the letter and have requested the publics help in identifying her. Can it be assumed that LE may have been holding this information close to the vest that has been revealed in this letter and that it is the long awaited for missing piece that LE has been waiting on and need confirmation to get warrents for searches and arrests.
The question of why would "she" deliver the letter to the news paper instead of the police is IMO a significant piece to this new puzzle.