I made a slight change to Karel that will hopefully make things a bit clearer - there were too many ways the conversation could "branch" so I pruned it a little. Also, as is noted in the assignment book for the case (sitting next to Jeffrey), there are up to five people that you may speak with, although some of them may not be specifically pointed to - you are going to have to consider what is said, and maybe act on a few hunches.
This is too cryptic to be considered a clue, but always consider not just what is said and by whom, but other clues that may be provided in the course of your interviews...
Also, in the assignment book it says reports are due by Sunday at 11:59pm EST - since there was a slight alteration to Karel's dialogue, I'm going to leave the quest itself up until then as well (it was set to end on Saturday originally).
I'm glad someone found Robert - he is one of those peripheral RPCs who is seen from time to time, and has been referred to (if not named) during events and fiction. His is an interesting story, though not one central to the major happenings.