I have no (good) ideas. I normally discount gun-grabbing theories as right-wing lunacy. I'm not convinced it's something the deep state really cares about.

The only thing I can imagine is that it was an act of terrorism with a demand that wasn't publicly delivered. E.g. Crown Prince MBS sends a secret cable to President Trump saying "there will be another one just like this if you don't sign the contract." I don't know if there are any historical precedents for something like that though.