Season Six of The Office began to reveal how the writers were losing sight of the show's trajectory. Notice how Pam is treated -- toward the end of the previous season, she had come to admire and even been grateful toward Michael after his artful maneuvering to get their jobs back and promote her to salesperson.
Then the wedding happens, which though a long time coming, nonetheless rounded out much of her character arc. But in Season Six, she's suddenly on the warpath, having forgotten everything Michael has done. On some level, that makes sense because of his treatment of her mother, but the fact that she's not in the least conflicted shows the writer's basically tossed out anything in terms of continuity. She's also rather disdainful of both Andy and Erin earlier in this season, which makes her character less than flattering after year of build up.
But this episode returns to some degree of character development that makes sense, just with Michael. The point after that first season is not so much that he's an idiot but that has life has been filled with disappointments and mistreatments, only some of which is the result of his needy personality. Those wounds continue to take their toll, resulting in someone with, if not a personality disorder, some profound quirks.
But Michael isn't stupid. He tries too hard to punch above his weight and, of course, usually fails miserably. Ask yourself if his frat boy antics would be rejected so easily and so often if he was actually more of a frat goy.
In "Murder," he's childish because how could he not be. But there's method to his madness. The often-cruel joke played on Michael is not so much that he doesn't understand people but that people reject him and therefore nothing he really does is going to impress them. But Michael was Dunder Mifflin's best salesman and, even under his chaotic watch, runs its best branch. It makes no character sense that he's so clueless about people.
And in this episode he isn't. I won't spoil too much, but let's just say Michael shows he understands psychology a lot better than people who tend to look down on him.
And that says a lot.