You know, I really find this guy interesting - one of my favorite flashback characters. Recapturing Kate seemed like an incredibly personal matter to him, but he was willing to let her go if she stayed with her husband. He attempted to hurt her, and then suggested that she euthanize him when he was on the verge of death. They had an adversarial but complex relationship, which was intriguing.
I think that although he wanted to bring her to justice, he also felt a strong amount of pity and sympathy towards her, hence his comments to Jack that no matter what she makes you feel, she can't be trusted, because she'd do anything to get away.

If season 4 continues with flashbacks as well as flashfowards then I look forward to seeing more of this guy! :3: