Are there any accounts written by torturers on their actions?

Henri Sanson, executioner of France, was part of the Sanson family who were the hereditary executioners for around 150 years. He wrote a book in 1847 describing his experiences and the experiences of his ancestors as related by family stories passed down over the years. (https://www.amazon.com/Memoirs-Sansons-Private-Documents-1688-1847-ebook/dp/B07DYBRSF7/ref=sr_1_4?dchild=1&keywords=henri+sanson&qid=1602259992&sr=8-4)

I know that there are also other books covering Charles-Henri Sanson, who was executioner during the period of the French Revolution, that describe his experiences, but all the books I've been able to find appear to be in French.

Anyways, the Sansons typically carried out state-mandated tortures and executions, but were never enthusiastic about it. The book I linked to above apparently describes their experiences and when they were particularly disgusted about the work they had to do. Executioners in France didn't have many job prospects, being semi-outcasts, so that was pretty much the only job available to them. Several Sansons took up practicing medicine as a side job (back when no formal education was needed) because they were unhappy with their primary job and the things they did.

I personally have not read the book I listed above, but I have heard selections from it on the History According to Bob podcast, which has been covering the French executioners over the past year.

Note sure if it counts, but Eric Fair is an Arabic linguist who worked in Iraq as a contract interrogator in early 2004.  He wrote a book on his experience, available from his web site.

He discussed this in a Washington Post article, quoted on this blog (and elsewhere):

A man with no face stares at me from the corner of a room.  He pleads for help, but I’m afraid to move.  He begins to cry.  It is a pitiful sound, and it sickens me.  He screams, but as I awaken, I realize the screams are mine.

That dream, along with a host of other nightmares, has plagued me since my return from Iraq in the summer of 2004.  Though the man in this particular nightmare has no face, I know who he is.  I assisted in his interrogation at a detention facility in Fallujah.

There's too much to quote, and some of it's quite distressing.  He goes on to say:

I failed to disobey a meritless order, I failed to protect a prisoner in my custody, and I failed to uphold the standards of human decency.  Instead, I intimidated, degraded, and humiliated a man who could not defend himself.  I compromised my values.  I will never forgive myself.

Dr. Miklos Nyiszli's Auschwitz: A Doctor's Eyewitness Account (ISBN 583122345)

The author talks of his participation as a means of survival and is not the easiest of reads.

The diary of Thomas Thistlewood, an 18th century slaveowner in Jamaica, records in great and vivid detail his regular torture, rape, and forced humiliation of 'his' slaves. The diary has been digitised by Yale University and is available at the website of the Beinecke library.

In the documentary, "All Watched Over by Machines of Loving Grace" by Adam Curtis (produced by the BBC), episode 3, there is footage from an interview in 1967 with a mercenary who tortured and murdered people in the Congo (approximately at the 30 minute mark). The same clip is included in this blog post by Adam Curtis which includes a lot of historical background for the documentary.

Joseph Desire Mobutu had seized complete control of the Congo and he moved against the rebels. This time though the white mercenaries switched sides and worked for the rebels. But they had lost Major Hoare, their old leader, and they rapidly spun out of control. The mercenaries committed horrific acts of violence against Congolese rebels and civilians. To the Congolese it was as though the ghosts of the horrors they had suffered under the Belgian King Leopold had been reawakened.

This is part of an interview with one of those mercenaries. He is remarkably open about both what he did and what he felt as he did it. You don't see anything, but what he describes is really not for the squeamish.

I do not know if the full footage of the interview is available publicly.

Pictures from the book "Drawings from the GULAG" by Danzig Baldaev, a retired Soviet prison guard. Depictions of the Soviet genocide.

In Melgunov's Red Terror in Russia 1917 - 1923 are several accounts of executioners and torturers going insane. He tells of a Bolshevik commissar named Mikhail Kedrov who was famous for making it a point to execute the children himself. He went insane.

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.

Since it has not been mentioned yet: There are quite a lot of accounts of the Holocaust from the point of view of its perpetrators. It does indeed seem as if there were some psychological problems (often in the form of alcohol abuse), but many perpetrators also seem to have found some way to justify what they were doing (orders have to be followed, it is ugly but necessary because they might kill us otherwise etc).

Another data point might be https://en.m.wikipedia.org/wiki/The_Act_of_Killing , which is a documentary about atrocities in Indonesia in the 1960s. But I have not seen that movie yet.