The paper considers two basic philological/historical issues. The first deals with the most important preserved Greek sources describing the preparation of the conspiracy against Nikephoros II Phokas and his murder (Leo the Deacon, Michael Psellos, John Skylitzes and John Zonaras). It examines their reliance on the lost sources known as version "A" and "B" of the biography of Nikephoros II Phokas, and refers in particular to the Short History by Michael Psellos. The second issue involves the relations between John Tzimiskes and Nikephoros II Phokas in the period from 965 (Tzimiskes' demobilisation?) until the murder of Nikephoros Phokas, in December 969, a time that was poorly documented in the said sources.