Who is the narrator, can she or he read minds, and, more importantly, can we trust her or him?
First Person (Central Narrator) – Thomas Fowler
Late in the novel, the police inspector Vigot explains to Thomas Fowler the logic of confessing one's sins. The penitent confessing doesn't always seek cleansing, as Fowler guesses. "Sometimes he only wants to see himself clearly as he is," Vigot tells him (4.1.28).
Fowler might not believe in confessing to a priest, but to us, his story has the feel of a confession. He admits to us what he won't say to Vigot or to others. He's more open about his faults and failings. He notes to us those occasions in which he's lied to others.
We may be able to assume, therefore, that Fowler is a reliable first person narrator. However, we also question how well Fowler knows himself. He's among the characters that he tries to deceive. So what's the answer? Hard to say. Perhaps Fowler is best thought of as a reliable, but limited and biased narrator—kind of like your one weird aunt.