Some examples can be found in the log book of Vasco da Gama first travel to India:
"Vasco da Gama ordered to torture two captured Arabs. With cool blood the Captain-Commander interrogated the unhappy prisoners, dropping on their backs the boiling mixture of tar and oil..."
From the travel log of Alfonso de Albuquerque:
"In Mascat (Muscat), Albuquerque ordered to exterminate almost all population, and to those who remained to cut their noses and ears."
It is not known who exactly wrote the log of the expedition, but one can be sure that
the texts were approved by the Captain-Commanders, since these were their official reports.
Many similar examples can be found in the 15-16 centuries travel logs.
(I cite not from the original travel logs, but from the book by Jules Verne, "Découverte de la Terre: Histoire générale des grands voyages et des grands voyageurs" (Discovery of Earth), who cites the original logs.)
Another rich source is the Malleus Maleficarum (Hammer of witches)
which is a manual to inquisitors published in 1486.
It is essentially an inquisitor's manual, and it contains a lot of "case studies", taken from the original logs of interrogations by inquisition.
(Until 18 century, torture was a normal, approved juducial procedure in many countries).
Of course the comment that inquisitors did not torture themselves is correct. But they were present and gave orders. Those executioners who
actually performed torture were probably illiterate and did not put their impressions in writing.