I also believe this was a “hit.” The killer knew how early to arrive...which tells me he knew about what time the husband would leave, so he had to be there waiting before that. He knew to wait until her husbands car had left. Although he had a gun, it seems he didn’t want to confront two people. He drove by the night before. He had to plan out the costume he wore. Luckily for him, there was no early morning trash pickup in the area to provide witnesses. Did he know that wouldn’t be an issue? Was the anniversary trip somehow a provocation that enraged someone?