The purpose of this essay is to systematize the information acquired to date on the determination and exact number of the letters written by Christian-Democrat leader Aldo Moro while a prisoner of the Red Brigades, and delivered by that terrorist group over the 55 days of his abduction (16 March-9 May 1978). The edition of Aldo Moro's Letters from the prison, edited by Miguel Gotor (Einaudi, 2008) is a constant source of reference for the first part of this essay, which debates Gotor's reckoning of the letters and messages actually received during Moro's detention. The uncertainty about this question stems from the fact that the appointed judicial authorities were not informed of all the letters issuing from the Red Brigades' prison. The second part deals with some new information concerning the timing of the delivery of some letters, and the upsetting discovery that a few writings by the politician, that have yet to be tracked down, must have arrived before March 29th 1978, the first known delivery date.