Maybe this becomes clear in later episodes, but I just finished reading Mindhunter which is about the development profiling by the FBI. Really interesting but seems like one of those experts would have been included in this mini-series. The book does address these serial killers and the FBI involvement as well as the development of the manual now used to classify criminals. Agent John Douglas was front and center and their work included interviewing those already incarcerated so as to learn from them.
If they were invited and declined, then that tells me something about this program.
I will watch a bit more and see if this aspect - the profiling by the FBI, is included.