@Deepvoid , I guess the FBI brought this guy in for having talked to a well-known suicide bomber. Talked to. They questioned him and then tracked him for a year, and he didn't talk to that guy again. Then he talked to some other radical, so they brought him in. Note that the FBI knew this because they were tracking him. They questioned him, did research, could find no evidence of wrongdoing, so they let him go.
Right now, everybody in this country has civil rights and the FBI can't arrest or hold people for "suspicion" of nothing. And gun restrictions prevent felons and people with mental illness from getting guns, but we do not have a National gun registration database (because of states rights) and we do not yet have any laws that prevent any "suspicious people" on any "watch lists" from getting guns, mostly because our Federal Watch List is so fucked up, PILOTS are erroneously on it and also because people have not actually DONE anything.
If there is an Order of Protection issued against you, yes, that wil trigger a flag in Illinois that will prevent you from buying a gun or ammo in Illinois to use to kill your spouse. However, that does not prevent you from driving 30 minutes to Gary Indiana to buy a gun and ammo, there, where the OofP won't be in the database. Yes, our system is flawed and no, there is no way to know that this "suspect" was going to do THIS.
Even if we ban "assault weapons" and high capacity magazines right now, Federally (which we have done before, which I would fully support), we would not be capable of confiscating the millions that are already out there. A ban would be a start, though. These terrorists are going to be using these as the easy weapon of choice in this country. However, sadly, it is probably going to take something like the attempted assassination of somebody for change to happen (the attempted assassination of Reagan is what brought on the last one). I mean, nobody cares until it affects Congress otherwise Congress is too in bed with the NRA.
Ultimately, though, the illegal guns will come in the same way as the illegal drugs.