Did you notice that when Monk was telling Kroger all about Hal, Kroger wasn't suspicious of Hal at all. But Natalie and Stottlemeyer were suspicious of Hal right away.
You might think it's because Kroger never met Hal in person, but Stott was also suspicious before he saw Hal in person (at the restaurant with the dead guy).
I wonder if it's because Stott spent two years working in vice, and because Natalie had to deal with some sleazies in her long period before she met Monk.
Monk was so blinded to reality that he couldn't really solve the mystery even though he was able to when Hal pointed the gun at him. It's so sad, Monk wanted to contact Hal even after he was arrested.
