Corrected entry: During Castle's time with the hot girl from the interview, just before Beckett arrives, he makes a comment saying that he found out who the killer is by something the girl said. Only problem is that he really didn't. When she said, after he asked how one guy got away, she responded with the line "I can assure you, it had nothing to do with me", before opening her dress and straddling Castle. By this time Beckett overhears them and breaks in, meaning that there wasn't enough time for the girl to actually tell him who the guy was. This also wasn't brought up or mentioned earlier, so Castle did not find out who the killer was; there's no way.