As so aptly stated by AlexB2, this is all about activists pushing their own agendas.  Having a Violence Against Women advocate oversee police investigations will result in; pressure on police to ignore the rules of evidence, and, attempt to  skew their judgement on the credibility of witnesses.  Without a credible witness there is no court case.  
Again, I note that within their 'exhaustive' research efforts, the author(s) have yet to take the time to ask experienced police investigators what issues they face.   How come?   Perhaps they don't like the answers they get as they interfere with the narrative they are promoting.   So, in the end, this is not a properly researched issue, rather it is a campaign based on a feminist ideology.