kidnapped girls unfortunately are still being held by boca haram. another american has just been detained in north korea. the u.s. state department says it is aware of these reports that the north korean government stopped him from boarding a flight in pyongyang. i want to bring in elise abbott, our global affairs correspondent. this would be the fourth american detained in the communist nation. do we know why he is being held? >> reporter: we don't, ana. all we know is that the north koreans are saying he committed so-called hostile acts against the government. he worked for pyongyang university of science and technology, which is, you know, interestingly the same university that tony kim, another american that the north koreans detained, was detained on april 22nd when he was leaving pyongyang. they work for the same university. we don't know if there's any connection, but cnn has spoken to people who have known this