Looks like we all pretty much agree at this point that the fact that Sarai was American had nothing to do with her death. We may not completely agree on how easy/obvious it is to spot Americans in foreign countries, but at least we tend to agree on the other.
At this point, the only question I find myself asking is WHY TK killed Sarai, not if. I'm not 100% sold on motive just yet, but really can't help but think he harmed her. This crime seems personal- and has always felt that way somehow- so I don't think the motive had to do with her nationality, religion, or (perceived) financial status. I lean towards thinking he thought the relationship was deeper than it was, and when she attempted to set the record straight, he snapped. I don't even really think he planned this out in advance. I think it was a heat-of-the-moment kind of thing, and I think he definitely panicked. Maybe he didn't intend to kill her, but flew into some sort of rage and before he realized what he'd done, she was gone. Don't we hear about that kind of thing here in the states all the time? If this was a crime committed on domestic soil, once most of us heard she'd last had contact with this strange Taylan figure, we'd have jumped to the same conclusion. That's my personal opinion, anyway.