Character Analysis
Our Hero, Arbogast
Milton Arbogast is less a character than a way to fake-out the audience for the second time.
Detective Arbogast is a private investigator hired by Cassidy and/or Lowery (it's never quite clear which) to get Cassidy's money back. Arbogast shows up in the scene directly after the sequence in which Marion's murdered and her body's hidden.
The murder of Marion is a shock not just because it's grisly, but also because Marion Crane was the main character. The audience shared her point of view. And she was played by then-megastar Janet Leigh. You just didn't kill the main character played by Janet Leigh. It just didn't happen… at least until Hitchcock did it.
Arbogast is introduced into the film to suggest a possible solution. His character is meant to suggest to the audience that maybe Psycho is a detective film, and that maybe Arbogast is there to avenge Marion's death and bring the creepy Norman Bates to justice.
Ha. Ha, ha. Not so much.
The Stab-Man Cometh
So you watch Arbogast interrogate Norman…and then you watch him sneak back to the Bates house to interrogate Mrs. Bates.
And then what happens? The clever detective gets gruesomely stabbed to death. The stabbing is done at the top of the stairs, and we get a vertigo-inducing shot of Arbogast tumbling down the carpeted staircase.
This shot is meant to mirror the viewers disorientation as they collectively shout: "What, the protagonist is getting killed again?"
And that bloody wet sound as the knife finishes Arbogast off? That's Hitchcock's witty little way of saying, "Ha, fooled you again."
Detective Arbogast's Timeline