I understand everything in the scene except for the car driving around. Michael wanted the confession out of Carlo to satisfy himself and to let Carlo know that he didn't get away with his deception. Otherwise, he just simply could have had him killed at any point.

The timing of the killing was perfect because everyone was gone from the mall and Carlo hadn't yet heard about the various deaths yet. (I wonder if he knew about the Tessio/Barzini plan?). The plane ticket was for Carlo to relax and get in the car. But I don't understandwhy the car was driven around. I don't think that they'd want to drive around choking a guy to death for everyone to see.

Also, what did they do with the body? By the last scene, Connie obviously knew that Carlo was dead. Wouldn't her first emotion be revenge by the Family?