“Taking Down Backpage: Fighting the World’s Largest Sex Trafficker,” by Maggy Krell (New York University Press)The final chapter in the Taking Down Backpage story has yet to be written.Prosecutor Maggy Krell offers a compelling account of her legal strategy in going after Backpage, a website that offered sexual services; some, Krell said, from girls as young as 12.Krell’s book illuminates how prosecutors build teams across several agencies to pursue complicated cases.Sometimes though, the objectives of law enforcement and the justice system collide. For example, the FBI had been using Backpage as a source for helping agents find people who had been trafficked.But the book was published too soon.