Cloudy with a Chance of Murder - S5-E2
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.
Correction: Whether or not Castle was able to simply deduce Haxton was the one man who resisted Coterra or she said it was Haxton, she had plenty of time to say one word before Beckett breaks in. In fact, when Beckett is at Castle' door she hears muffled voices, so there was a lot we didn't hear from the phone call to busting in.
Bishop73
That was Castle trying to get her off. He was resisting her you know. Why would she say "oh, by the way it was Haxton" as she was trying to seduce him?