Corrected entry: Upon discovering Alexis has been abducted, no one thinks to call her mother Meredith. Even with Castle's dislike of her, surely she deserves the right to know something has happened to her child. And since Castle frequently paints her as an over-the-top drama queen, one would think he would prefer the drama of simply telling her the truth, rather than not telling her and having her find out that he didn't tell her.
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.
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?
Correction: I'm pretty sure Castle was smart and responsible enough to tell Meredith what's going on. Just because we don't see him do it or even bring it does not mean that he never did. Also, she wasn't important to the story, and maybe she was too busy to actually come out. Even if she wasn't, what could she do to help?