Vengeance Vito Corleone style will get you nothing but a prison sentence. You need to flesh out the context of the situation you described or we’re all sort of shooting in the dark re trying to give you useful advice.
As a verb, rape meant “to steal from” or “to strip of possessions, longings, or value” before it meant “to force sexual intercourse upon.” I’m not near my OED (as I keep it at the public library), soI can’t check, but I’d not be surpirsed to learn that violate was synonymous with the current usage of rape before the latter word took on that meaning.
Have you considered called the cops and getting him prosecuted for rape? Spending a couple dozen years in prison isn’t exactly a basket of roses.
No punishment that you can mete out (short of killing him) is going to compare to spending decades in jail. If you were serious about making his existance a living hell that’s what you’d be concentrating on.
Evidently there was a duplicate thread. I’m just posting here what I did there:
Not exactly sure what you’re looking for here, but let me just start off that YOU shouldn’t take things into your own hands. Your niece has already been through something horrific, it’s not going to help her to have gone through that and then lose her uncle who cares for deeply to the system for some years.
Can I assume that she will report this? I hope so. And if, for whatever reason, the authorities become a dead end, how about going to his commanding officers—not just his immediate supervisor? I’d write letters all the way up and down the chain of command. Obviously, this piece of shit belongs in prison. I wouldn’t be surprised if the “friends” aspect of this would qualify him for considerably more serious punishment. I’d hope so.
The more important thing to remember, though, is to make sure you stay around to support her.
Good luck to you both.
I understand you rage but you’re niece is an adult now. It’s up to her what she wants to do. Your only job is to be the “rock” that she may need to lean on.
Also, stop being that typical man women are always bitching at us about. You don’t need to “fix” it for her; just be there.
You don’t do a couple of dozen years in prison for rape. You don’t even do one dozen years. 
Snug, I have no advice, except to say don’t take the law into your own hands. You’ll either get yourself thrown in jail or get yourself killed. Neither will do your niece any good.
Do get the authorities involved.
From the Latin:
Rapio (v): To seize, to snatch, to tear away. Also the source of words like raptor and rapture
violo (v) To injure, do violence to.
violentia (n) violence
violelentus (adj) violent
violatio (n) injury
violator (n) injurer, one who does violence
I should clarify: my niece was raped three days ago. I did not learn about this until this afternoon. She did not go to the police or complete the rape kit. She was discouraged from doing this by her father, who didn’t want her to besmirch the family name. We couldn’t have that.
So, yes, I know the “proper” way to go about this, but I’m afraid it’s too late: it’s all he-said-she-said now. So I’d like some improper ideas, please.
And, j666, I can’t thank you enough for putting me in my place. When I thought that nothing in the world could possibly make me feel worse, you succeeded. Congratulations.
Rape can get you life in prison or even death under the Uniform Code of Military Justice:
The father is a piece of crap. I don’t know what advice to give you. I would try to contact his CO anyway and tell him what happened. I’d also peel some paint off the dad (is he your brother or or brother-in-law?).
A few years ago, my wife’s teenaged niece was raped. To make matters worse, she got pregnant and had to get an abortion (which she kept secret from the family for over a year). I know the feelings your going through. It’s incredibly frustrating. Rape is one of the most difficult crimes to get justice for.
Wow, I’m sorry to hear that her dad reacted like that. 
At the very least, you may want to help her get the morning after pill to protect her against pregnancy from this. http://www.not-2-late.com has info on that if you want to try to talk to her about it.
Not under the civilian justice system, but the UCMJ is a lot more hard-ass. Leavenworth is no country club either.
Yes. In addition, that Thing and his co-Things if convicted would probaly never be able to hold a real job again. That would make his life a living hell.
Also if he’s convicted, he won’t find prison to be all that nice.
Encourage your niece to press charges. I know a lot of victims are afraid to face their rapist, but it’s very possible that she might not have to testify face to face.
Strongly suggest that your neice get into intensive therapy. If she doesn’t, she’ll prolly end up really psychologically messed up. I know a girl who was raped in a dentists chair, and slept with a dude she didn’t even care for even as a friend…freaking weird…she also has a ton of psychological issues…too too sad.
Well I think it depends on circumstances. He may not get as much as a “stranger predator” type of case…but b/c she was drugged AND gang raped that does mean that its a bit more serious then a " oh I misunderstood. I thought she wanted to have sex" sort of thing.
Something like this incidcates that the perpetrator is probaly an extreme fuck up and is prolly a full blown sociopath. I have to say…I do think that in cases like these, the THINGS who commit these sorts of fuck-ups really need to be put in a mental hospital for the criminally insane. I’m sorry, but most of them are honest to god predators who are just so fucked up they can’t function in society.
Despite the responses to j666’s posts, I think this is what she was countering (albeit early). While rape is certainly different than other sorts of crime in terms of violating personal space and creating a lasting association between pain and one of life’s potentially most pleasurable acts, in terms of the legal system it’s been suggested that victims would be much better off filing charges for ‘assault with a blunt object.’
Victims and victims’ rights advocates tread a fine line – it’s both important to let rape victims speak out and to raise awareness about the prevalence and lasting consequences of rape, but doing so risks stereotyping victims. So if someone’s testifying against a rapist and explaining how she’s attempted suicide ten times and can never trust again, it shouldn’t affect the woman who’s made peace with what happened… but it does, if only when people around her presume how she should act or feel.
Several posters implied or stated that the niece had better report the crime, if not for herself then for other potential victims. While this would be the first step in an ideal world, as the OP’s follow-up post suggests, it’s hardly that simple.
I say that she should still go to the police now - if she was drugged they may still be able to collect some evidence via blood analysis (I am NOT knowledgable about this, but I do know some drugs will still be detectable 3 days later)
Also being naieve I guess, if his friends participated, some info may be able to be garnered from them, enough for this to fall out of the sphere of he said she said scenario 9on the other hand of they co-ordinate their stories…)
Your niece needs to go to the cops, and probably the military police as well. It would be great if you go with her, for moral support. You can’t help her in giving testimony, but she needs to know that some men are still worthy people. I don’t know if she still has the drug in her body, but she needs to at least try to work the justice system. Do bring it up to the military police, and if possible talk to the scumbag’s CO about this.
I can’t believe that people STILL have this “it was all her fault” attitude about rape victims.
Out of curiosity per the OP’s description assuming she was not physically beaten (so there would be bruises etc) how, as a practical matter, is a charge of rape going to be substantiated with no witnesses or physical evidence?
Per the OP, the cretin invited other parties to “partake”. Perhaps one of them could be persuaded to testify.
She might have bodily fluids on her clothes or other possessions, or there might be other physical evidence on her person or possessions. She might have left physical evidence at the scene of the crime. There might have been eyewitnesses, or someone who heard something about it afterwards. Perhaps Scumbag invited someone to partake who refused to be a rapist.
However, the longer she waits, the more chance of evidence or witnesses or memory disappearing.
Go to local law enforcement; now.