None of them were paid - they were simply provided with PDFs of the files and asked for their opinions. Newspapers do not pay for such things, and they don't need to, there are always plenty of people ready to opine. For better or worse, they are the same experts that would testify in a court proceeding and yes, they pretty much all have actual policing experience. (How do I know this? I know a couple of them and did research on the rest.) They got the interviews and a few other things, although