Found someone's unrecovered deer

What are the options/obligations to a hunter/person has who happens upon a dead deer that someone obviously shot and failed to recover? We happened across a nice buck that looked to have been dead for about a week. We took a picture of it but left it undisturbed were it laid because we didn't know what we could/should do about it. I'd like to take the antlers if I can... (if it's even still there).

Just in case it's different for public or private land, the deer is on public land.

Thanks.