[This letter was scrawled anonymously and left on the doorstep of the then-mayor of Manehattan's home overnight. Whether it was written by the Blood Mage of Manehattan is unknown. Nothing indicates the author of the letter beyond the paper's poor quality and that it did indeed come with an equine kidney. The Blood Mage did admit to writing letters to taunt those who worked toward her capture, but it is unknown which ones are the authentic pieces. She was known to tease in her interrogations. In the present day, it currently resides in the Canterlot Archives. For its vulgarity against Princess Celestia, it is illegal for any non-royalty to access or acknowledge its existence. Reprinting it and quoting it is strictly forbidden by Equestrian law.]
From Tartarus.
Mayor-Stallion,
Sir
I send you half kidney I took from one whore. I preserved it for you. I licked the blood and bile from the other piece and threw it into the sea. I might send you the bloody knife and crystals that took it out if you wait a while longer.
Signed,
Have your city catch me when they can, Mayor-Stallion. Spit on the goddess that allows you such power.
[Various speculation at the time of the investigation suggests it is highly likely the letter is authentic. The syntax is equal to what the Blood Mage was capable and many of the later victims were missing even more organs. The murderer also confessed to various illegal cannibalistic crimes against the later ones that would have been slain around the time the letter was deposited.]