It’s easy to forget that a central job of the Embassy was to support Saudis going to school and they had been providing this service formally and informally for

It’s easy to forget that a central job of the Embassy was to support Saudis going to school and they had been providing this service formally and informally for many years and to many people -- the vast majority of whom went back to their community with an expanded outlook on life influenced by the tolerance and social freedoms of spending some formative years in the west. If the Embassy didn't know these guys were terrorists (due to the for-eyes-only information stovepipes which affected the FBI just as much) then they would treat them just the same as any Saudi in the USA -- on-board them into the US (advice on accommodation/where the mosques are/where they serve hallal food/introduce to other Arabs in the community/play cards/etc), then check up on their situation from time to time. And then try to hide the fact they had any contact at all after the passports turned up in the wreckage. Not saying it’s impossible for any specific bad actor collusion by some individual(s)/institution(s) with overlapping goals - just that proof there was Embassy contact and some support for these terrorists is not conclusive evidence because the same could be said for several hundred thousand non-terrorists.