The killing of the dog here, seemed very personal, and rage fueled. Also, a random person wouldn't know if the dog could have attacked.
An acquaintance could easily meet up in the park. Do it quickly, and leave.
I never thought that the Moscow, Idaho murders were from a personal friend, I always thought of those as a psycho killing, not unlike the "Florida Sorority" house killings by Ted Bundy. And I definitely don't think that this was a transient killing.
This one seems planned out, like those killings, but also personalized, like there was true animosity.