Here's how I think RJ guessed PJ's list of suspects: 
RJ told Lorelei that he shook hands with PJ. He then sent her to meet PJ, knowing PJ might extract that information from her at some point. RJ has the means to track down the people PJshook hands with. RJ's research leads to the list of 7 names, before PJ even knew about having shaken hands with him. When RJ finds out Lorelei let it slip about the shaking hands, he records the video with the list. Then he only needs to get PJ's research to confirm that the lists are the same. He only gave PJ the video because he knew his guesses were correct. Had RJ's guesses been wrong, he could simply not release the video and proceed with some other plan. We don't know how many alternative plans RJ had, we only get to see the one that succeeded.