How do you know? How do you explain to a judge that declining an invitation makes someone guilty? Unless the judge sucks then he/she cannot grant a warrant based on that. If the judge does then we have a bigger problem, aka a corrupt judiciary. On the other hand, if one of the people who doesn’t cooperate with the investigation happened to know the kids then that’s a red flag, no? Maybe there was some issue with the girls or a member of their family?
Means, motive and opportunity. Without all 3 it’s hard to convict someone of a crime.
Threats overt and covert are made during these chats, the coercion factor is high, and they work things so that the citizen feels heavy pressure to “volunteer”.
They are not using the volunteers to find the perpetrator, they are narrowing the group of people they need to strongarm into getting their firearm tested and inspected, while they are inside the courthouse or governmnet building, where some subtle interrogation can be applied without the bother of a warrant.