I see no evidence that he has a conscience.
You are exactly correct. It appears to me that Vang is a sociopath. From the remarks of his family, I have my concerns about them as well. Note that they were proud of him and what he did.
This is a very human thing in a tribal culture, but not acceptable in the U.S.A., or in any civilization, which must overcome tribal loyalties.
I also suspect that Vang killed before and got away with it. Except for a few breaks against him, things he did not expect, he could easily have gotten away with these horrendous crimes.
I mean "conscience" in a broader sense, more like someone is watching and making a list of the good and bad things that you do (Santa?). Probably more like Karma then any active voice giving guidance, I know this POS has no inherent sense of right & wrong. I just have to hope that someone is keeping score on this bad apple.
Regards,
GtG