Now that you mention the marital discord, it definitely becomes more clear. That said, I believe it is so hidden because of Jimmy Stewart's true character. I find it hard for the Boy Scout Jimmy Stewart to have marital problems, thus the on-screen performance becomes muted. Here lies the folly of major Hollywood stars. Perhaps an approach akin to David Fincher's Zodiac was in order: through strict repetition of anti-martial action -- Zodiac is to obsession as Man is to male dominance in times of stress -- the martial strife is palpable. By dropping us in the action, Hitchcock cannot defuse my preconceived notions of Stewart's good ol' boy persona. That said, the climax of this movie is absolutely amazing, and there is something poetic about the boy being held at a chapel. Hitchcock had a way with portraying evil in a way that was ahead of his time.