We all know that Bitcoin is also popular to criminals because they can use it without exposing their identity. It will be more convenient to them to use Bitcoin so that they can hide their identity. Do you think that terrorist groups like ISIS use it for their transactions?
I don't know but well maybe because how can they buy drugs without license and it is illegal to just carry or jump over in many countries , I think they used the deep web and they transact and buy some illegal stuffs and I think many terrorist doing this.