It just is so bizarre to me that none of them, as an individual with their own sensibilities and conscience, decided to report this to the authorities. It's clear that the daughters and quite possibly the mother were abused and vulnerable and therefore not strong enough mentally/emotionally at the time to do so themselves, but it is an absolute no brainer that if you hear first hand about something like this it is a CRIME and should be investigated by the AUTHORITIES so that this evil man could not do it to anyone else.
The only explanation as to why none of them did (and not one of 1006 cases were reported either) is that they were members of a high control institution which discouraged reporting to the secular authorities, whether in writing or not, and this is a fact this organization will not be able to escape from.
BTW The scripture in Lev 5:1 about reporting another's sins is applicable to a court of law, the only court of the land in that context, not just a 'spiritual' court. So if they knew about such a crime, they were under obligation to report it to the legal authority of the land even by their own scriptural reasoning.