Hello everybody--what should I do?

I need to advise my friend on what to do about some photos she found. The photos are of two people she knows performing sexual acts. One is about four years old and the other is in his seventies. This guy should be put behind bars immediately of course but only his arm and hand and private parts are shown in the photos. She knows for sure who he is anyway. She says the parents are weird and won't do anything. What organizations should she get advise from? Should she go to the District Attorney? She needs to take the correct steps so that he doesn't get away with this.Thanks for your answers!