He was investigated and questioned by the FBI TWICE prior to the gun dealer dropping a dime on him. His Father has extremist views and has a cable access channel in Cali (if I remember correctly), that promotes an extremist ideology. His Father also claimed and or ran for president of Afghanistan. His Father is a nutcase. The apple don't fall far from the tree and children live what they learn.
The shooter worked as a security guard and had to qualify yearly as well as renew his licensing yearly. He bought his guns legally even after being investigated by the FBI.
The FBI questioned his ex-wife who allegedly knew about his erratic behavior (he beat her) but never reported it. The FBI released her and now she can't be found. Unless of course you head to the middle east, where she is more than likely being de-briefed by ISIS/ISIL/etc and getting ready to be sent back to the US to instigate another unstable individual with extremist views into doing something terrorist-like.
The No-Fly List is arbitrary, lacks due process and has little in the way of appeal. It also shifts the burden of proof on the accused instead of the state.
There is no published criteria for being placed on the list. Once you get put on the list, there is no due process available for correction of errors.
They can and will put you on the list if they don't like things you say. Then you will pay hell getting off that list. Abuse will be rampant. After all, if someone doesn't like gun owners for any stupid ass reason that gun owner is screwed seven ways from Sunday. Anyone who believes the gov't is there to help them has a mental illness.
In the end does anyone really believe that if someone is on the No-Fly list that they won't be able to get a gun if they want one? *cough* Mexican border? *cough* Extremists got fully automatic AK47s into France, duh.