> It is not known how the US government has determined that North Korea is the culprit
Of course it's known. The same way they established that Iraq had chemical weapons. The method is known as "because we say so".
Are you joking? I thought it was well established that there were chemical weapons in Iraq we just only found weapons designed by us, built by Europeans in factories in Iraq. And therefore the US didn't trumpet their achievements. In the case of Iraqi chemical weapons, the US established that Iraq had chemical weapons not because they said so but because Western countries had all the receipts.