I flirt with her at first, telling her I can see why he would want to stay home when he's got her. (1.2)
Rob's primary interrogation tactic—one that many cops, at least those on the Dublin Murder Squad use—it to manipulate their subject to get him closer and closer to a confession.
"Please let me stay," Rosalind said, lifting her chin. "Katy was my sister—whatever happened to her, I can… I can listen to it." (3.147)
Even though we don't know it yet, in Chapter 3, this is Rosalind already starting to be manipulative. She's pretending to care for her sister, but all she really wants to know is exactly what the cops know, and to find out if Damien did exactly what she wanted him to.
You get people like this in every investigation, people who end up wasting huge amounts of your time with their compulsion to say whatever they think you want to hear. (3.210)
Sometimes people tell cops what they think they want to hear in order to get them to do what they want, but it seems likely to us that sometimes people tell cops what they think they want to hear because, um, cops carry guns and have a ton of power.
"[Rosalind] was sick of her dad bossing her around. I think maybe he hit her or something." (7.34)
Rosalind's cousin Valerie is telling the truth here, but she's only saying what Rosalind told her. Of course Rosalind would tell her that her dad hit her—she wants to manipulate people into thinking that she's abused at home.
"I guess I'm a bit scared of [Detective Maddox.] She's so aggressive." (9.96)
Rosalind wastes no time trying to subtly turn Rob against Cassie. The sad thing is that Rob is an adult, and Rosalind is only seventeen, yet it works. She has him wrapped around her little finger, and she continues to manipulate him during this entire conversation.
"We've both been having a hard time," Rosalind said sharply, "but one of us has to act like an adult instead of like a stupid little girl." (9.227)
Rosalind manipulates Jessica, her younger sister, too, but she's a little, um, less gentle with her tactics. If she's passive-aggressive with Rob, then she's aggressive-aggressive with her sister.
"Hey, we all know what she needs," I said, "but would you want to get close enough to give it to her?" (13.125)
Rob mirrors Cathal's reprehensible misogyny in order to manipulate the guy into thinking Rob is an ally. He's being a "good cop" by basically pretending to be a rapist. Classy.
"They all believed him—all our classmates, all our mutual acquaintances, which added up to just about everyone I knew. People who were supposed to be my friends." (13.166)
Cassie's psychopathic college boyfriend is so good at ruining at her life because he doesn't just manipulate her, he fools all of her friends, thereby turning them against her, too.
"You head it up. He thinks of women as the source of sympathy and approval; I'll pat him on the head now and then. He's intimidated by men, so go easy: if you push him too hard, he'll freeze up and want to leave." (20.20)
Cassie is good at reading people, and she uses this skill during Damien's interrogation to coach Rob on exactly how to behave to the get the answers they need from Damien.
"It was my idea," Damien said quickly. "Rosalind had nothing to do with it. She didn't even— At first she said no." (23.95)
Rosalind is so good at manipulating Damien that he doesn't even realize he's doing exactly what she wants him to do. It's impressive, if also impressively terrible.