I can understand why some are doubtful this is BG. When I think of the person who committed this crime, I imagine someone methodical, calm, prepared and focussed on a target; and the recording sounds deep-voiced and in control. Someone like BTK who would seem normal on the outside. Based on DN's criminal history and these recent incidents, he seems impulsive/lacking self control, openly angry or "off" to everyone, and more like a spree killer.
If he did commit this crime, I could see it being a spur-of-the-moment decision when he originally went to the park to de-stress after breaking up with his wife (basing this on his social media re: the outdoors as stress relief and the timeline).
I noticed that post with the picture of the woods and then the pill below it too and found it disturbingly interesting. I thought to screenshot it but then got sidetracked.... now his profile is gone.