Why the charge did not go off:   It is actually not that easy to ignite it, given the conditions. Does not mean it could not be done. Just not easy to do--might need several tries.

Also, the handwringing about obvious signals missed is not justified.   All sorts of noise in intelligence operations. Sounds very like the favorite topic of some lefties that either FDR knew about Pearl Harbor in advance--- or it should have been detected by intelligence.   It ain't necessarily so.

I'd still like a direct quote by the father that his son would be involved in an al-Qaeda operation.    Have never seen one.   Father's main concern appears to be son hanging around with undesirables, and father wanted assistance in bringing son home.   Not a smoking gun.

Closest I've seen to smoking gun is the UK refusal to let him land there, since he was applying to a non-existent school.   Possible idea:   anybody who applies to a non-existent school should have to prove the school does exist--or lose all flying privileges anywhere in the world. This obviously would require close contact between intelligence operations of various countries.