It seems that it would be useful to know how far into the park the carcass was found. The article is fairly light on information and really leaves it open to speculation.
He was either on his or his neighbors property when he shot the deer and tracked it into the park. Then, finished the animal off and got some sweet pictures for the 'likes'.
Or,
He reasoned that he could push the boundary a bit with no likely repercussions and still get the 'likes'.
Either way, I find it difficult to believe he didn't know what side of the line he was on. It is too easy to use highly accurate gps mapping and when you're close to the border, you know. Anyone who hunts the edges has inadvertently left the property they started on. It's what you do when you realize that matters. The pull of the chase is strong and some can't say 'no'.
Posting pictures of an animal with a background that can identify you as being on ground where you do not belong is idiotic. That is baffling. The same thing happened with some CPW employees and a big bull a few years ago. They trespassed, killed an elk, and posted pictures of it. The carcass was found and they were convicted.
Unfortunately, the jackwagons that poached two bulls in Rocky Mountain National Park, and another up the Poudre Canyon, don't seem to have done the same.
Back to Greentree... If he did shoot the animal legally and had to pursue it into the park, I see no problem with that. Illegal but morally sound. I know that I would be bummed if I lost an animal to an invisible line. It's easy to armchair quarterback that one...
If he shot from private property into the park boundaries, that is more challenging to forgive.
If he trespassed first, and intentionally, that's greed. I see little possiblity that if he (and anyone else) did trespass it was unintentional.
As far as I can tell, there is not enough information to make a judgement call as an outsider.
Also, I don't think it matters what animal it was. Mouse, coyote, deer, whatever. If it's out of bounds, it's off limits.
That's my take.