Father Beheads Daughter's Rapist: Hero or Monster?

The question about the "rightness" of vigilante revenge definitely comes up after a father, an ex-South Africa rugby star, went on what looks to be a revenge killing spree, using an axe to murder three men he believes gang raped his daughter and gave her HIV. One of the victims' heads was found a mile away from his body. One of the two other men, also killed by axe, was nearly decapitated as well.
For anyone who has a daughter or a child, it seems a rightly served form of justice on men who would commit a heinous and violent crime against a young girl, especially leaving her to fight a deadly virus for life; however, this string of violence at the hands of a rage-filled father also reminds us to consider that taking the law into our own hands might not always work out how it should.
First of all, there is the matter of the gang rape, which is still alleged. It doesn't sound like anyone was picked up, arrested, or charged for the crime. Not suggesting the rape didn't happen. Not at all. If it was my kid who was raped, I'd have no problem taking her word for it. I could see many, many people immediately going after the rapists named by their own daughter.
But what if this father killed the wrong guys? What if, in an impassioned and murderous rampage, he hacked up someone he thought to be one of the rapists, and what if he was wrong? Then the story isn't so heroic anymore, is it? That's the purpose the courts and DNA tests and finger pointing in a courtroom serve. Everything else aside, you want to get the right guys. However, this is what we don't know when a person goes after people without the law behind him. The father is due in court tomorrow, where he will face three charges of murder and one of attempted murder for a fourth alleged victim who escaped. He is accused of stalking his victims over several days before hacking them to death with an axe.
Do you think this dad did the right thing or should he have stayed on the side of the law?