1-I - I don't envy your position. From other posts, I gather that you live somewhere in a rural town in central/southern Utah. Having grown up in a very rural town in Idaho, I know hunting is viewed differently in those parts than in the city. So are game laws. I say this not to excuse the illegal behavior you describe, but to let you know I understand the culture where this is considered acceptable. I actually think this ties back to the other thread on hunting as a right vs. priviledge.
Where I grew up, it was almost standard practice to make sure all the tags in the party were filled - no matter who shot the game. My Mom tagged 3-4 deer and has never fired a rifle. My brother tagged deer he never shot at. Whenever we hunted, I let everyone in the party know that my tag was not available for the "group hunt". It never set well with me. But then again, this was a town where most local ranchers considered pronghorn "Mexican food" and would pop one and drop it off in front of the run down camp trailer where their migrant workers lived - and do that once or twice a month throughout the year to keep them fed. The point is, then, game was considered a resource that had no end, and was available to all for the taking, laws or no laws about it. As long as there were game to hunt, there were plenty of tags and plenty of animals and no-one there complained or turned people in. The F&G turned their heads to the stuff of "tagging out" deer - at least the deer were tagged and not dumped in a ditch, or more recently, a car wash.
As I look at how game has become more scarce, and hunting demand has shifted in balance from subsistence, shoot anything approach, to quality hunting experience and higher demand for trophies, it seems like most of the hunting community has changed. It then becomes much more bothersome when people do what you have described. But there are folks still stuck in the older, shall I say, looser interpretation of the law.
Its very easy to come on here and say "nail the sucker! He's a freaking poacher." and he is. But having grown up in that culture, I would most assuredly think that your friend does not see this as poaching at all. He probably is a fairly ethical guy and sees nothing wrong in this. He is probably a guy who would turn someone in for shooting game out of season or other game violations. But this one is embedded in the culture.
I would suggest that you talk to the guy about it. You won't even have to bring it up. Everyone likes to tell hunting stories - just ask him. Before you turn him in, let him know that this behavior isn't fair, isn't ethical, and is illegal, and makes him a poacher. Let him know why his practices impact you, and other hunters, and also his family. And let him know that while it may be culturally acceptable in some groups, it is not legal. Period. I'd talk to him first though.
If you call DWR, you really don't need visual proof. You will be interviewed about it, and then they'll confront him about. They will interview him, his wife, and kids that he filled their tags. They will either lie about it, or will break down. Depending on the kids' age, they will probably crack and give the DWR all the info they need. That way they are incriminating themselves.
The other side of things, and depending on the CO you get to investigate - is that they may view this as there are 4 (or however many) dead deer. Each deer has a valid deer tag attached. The animals were not wasted. And who shot them is a he said/she said situation, and there are probably worse game violations to deal with than this one.
Its a tough one though. Good luck.
Disclaimer here: I do not condone shooting other people's deer, and I don't do it. My family did it over 20 years ago and I never condoned it, even as a teenager. It is another form of poaching - no matter that some people don't consider it illegal. It is. And shouldn't be done.
