It's Lison's brother the bounty hunter.
PJ shook hands with him and instantly knew he was a cocaine user, which is why Lorelei mentions it because it was the only memorable handshake of the entire series. The Tyger poem relates to Lisbon's struggles in dealing with finding out her brother has been usurping power and police information to become a serial killer so she's connected with Jane in that way because they are close and it was her own family that killed his. He's also handsome and smooth. Robert Kirkland might suspect it even that's why he's playing games with Lisbon to get close just in case he's right, and he probably wants to make sure she isn't helping him. Why else would he want to buy her a cup of coffee? Like RJ and his cohorts really are worried about stupid Lisbon, and I'm sure it's not about just trying to get a date, he is genuinely concerned to explore the angle that he has just discovered.
