I can have evidence showing that she gave him her money, that she prostituted herself for him and that he beat her but if she does not want to file a complaint and if she is comfortable with that, then there is nothing that we can do. It is the same as in domestic violence cases.
There are some investigative techniques. We could use a double agent, for example. These are things that are being done, but in such cases, the sentence is lower than it would have been had there been a real victim.