Domestic violence is a crime that usually occurs/happens/takes place between four walls. [or...within the four walls of a household, generally.)
(it´s my personal style, but I favor "happens/takes place'' here)
That´s why normally there are no witnesses, and when there are, most of them don´t want to get involved. The Portuguese saying that “entre marido e mulher ninguém deve meter a colher" (it´s not wise to meddle in a couple affairs, let alone their fights/quarrels/spats.) or the English saying “mind your business”, unfortunately this saying strictly followed, will mean indifference/apathy towards the life of a human life.
Despite recent campaigns, many people accept domestic violence as something seemingly normal. That happens because usually the offender cultivate (on purpose) the image of good parents/fathers/an excellent family man, and consequently a good partner. And many times a role model/a helpful member of society/his community (as a means of justifying his bad deeds.
So, this was just to illustrate my point/just to make my point; wich is, a domestic abuser is difficult to spot, just try to ask someone close to one (a friend or a family member/a relative) what kind of person he is or how he is like! More often than not, they will deny that he is a violent person, an even swear that he is as cool as a cucumber.
[..."to make the point...would do, as well.]
Sometimes the wrongdoers will get to the point of smearing the victim´s reputation, for instance, saying that the victim was drunk, that was verbally attacked and other things. All that to undermine the victim’s access to justice or to make others believe that the victim is a liar, or twisted the account of facts.