In the Penal Colony
Symbolism, Imagery, Allegory
Depending on how you read the penal colony itself, the officer will change, too. In Warren's view (see "Reading the story allegorically" above), the officer is something of a priest figure, and definitely the hero of the story, standing up for his true beliefs. If the penal colony is a totalitarian state, the officer is just a thoroughly brainwashed goon who buys into the system and kills people with no bad conscience. In the "traditional religious society" reading, he can be a priest-like figure or a "true believer."
On the other hand, if you want a much more dramatic allegorical reading of the officer, you could see him as a Christ figure. The machine, with its excruciating and very long procedure, and the wounds it inflicts on the body of the prisoner, might make you think of the crucifixion. Plus, like Christ, the officer sacrifices himself and suffers an excruciating death. Of course, if you want to go this route, the question is "For what does the officer sacrifice himself?"