Couple must have been confident to not go to jail (spoiler)
The logical side of me kicked in once the gunshots were fired. The rich couple must have been pretty confident about covering up a murder, especially one as messy as that. People saw the 4 of them leave the bar that night and the little girl next door saw the character that was killed, and the neighbors house seemed to be close enough to hear the shots. It was the night their dog disappeared as well.
It's not made clear, but I got the impression that this was just another night of typical activity for this couple. Couldn't get away with many murders like that before la policia would catch up to them. Jail would be a drastic switch to their lifestyle!