The speaker of "Informer" is a paid spy whose subjects are already dead. He meets two men who were hanged that day on a narrow ledge, and the three of them simply walk up and down, like men pacing a corridor while they wait. It is calm and strange, and nothing about it feels like an interrogation.
The second half turns bleakly comic. "The commissioners" pay him to report on the dead, which suggests an authority so hungry for information that it keeps watching even after it has killed. His equipment is shabby: a "theater of clerks," two mousetraps, and a "rank-rot mouth." The clerks sound like a show of official procedure, the mousetraps like crude tools for catching secrets, and the rotten mouth hints that the speaker is tainted by his work.
The mood is eerie, dry and quietly grim. The speaker never says how he feels, but the flat tone suggests resignation, or even shame, at serving a system that has nothing left to take.