Give us your synopsis.
My unlearned opinion would suspect that the nuclear material would have come from North Korea of Iraq.
The heeyoouuge material lift from Iraq to Syria prior to the invasion has not (to my knowledge) been accounted for.
Some of it certainly appears to have worked its way to Libya.
And NK is a known proliferator who is probably looking for other working partners that can work with them to develop nuclear weapons.
I can find no reason to believe there would have or could have been a transfer of nuclear material to Syria from US sources. No way that could have been kept quiet, and Syria probably doesn’t have the buddies or contacts to pull a NUMEC-type deal.
That’s my take. Probably wrong.