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As NTSB mentioned, U.S.-registered airlines operate under Part 121 of the FAA regs, while foreign airlines operating into the U.S. operate under Part 129 of the FAA regs. Most simply stated, Part 129 kicks things back to regs of the foreign airline's country, which may not (and often don't) mirror the FAA's regs. Under Korean regs, the crew may not have been required to submit for post-accident testing.
I understand that the law may exempt that, what I meant by
should is that I don't believe that this is a good idea, nor particularly logical, given that the accident location is more important than the operator's base.
I can see how from an FAA point of view, they would have an interest in having US based crews tested post-crash overseas, but I don't see that in order to get that situation they would have to give up the right to test overseas crews in the US post-crash.
I assume if there was any indication of inebriation that the police could demand a test, as opposed to some FAA regulation, correct?
Arguably, flying a servicable aircraft into a seawall in perfect weather could constitute 'reasonable suspicion' for a San Fran police officer, even just to eliminate it as a factor.