Al-Qaeda trained in Afghanistan, Sudan, and had ties to people in Pakistan. 15 of the 19 hijackers were Saudi, although 3 of the 4 pilots (who were the leaders and apparently the only ones who knew the plan was a suicide mission) were not Saudi; those were from Egypt, UAE, and Lebanon.

In the immediate aftermath, as details first came out about the identities of the hijackers, there was a lot of anger towards Muslims in general and Saudis in particular, especially after it became public that the Bush administration had allowed several members of the Saudi royal family to fly out of the US while all US airspace was supposed to be closed. In the intervening years, whether because of active rehabilitation efforts by the Saudis or by wider acceptance of Al-Qaeda as a pan-Arab organization, I feel like that anti-Saudi sentiment has cooled.