Local (state level) controls will work.
Mass shooters usually do their deed in the community where they live. Often at their schools or workplace. In other cases, at local theatres or churches or malls. The Roseburg shooter did it at his school (Umpqua Community College).
When you buy a gun, you have to show ID showing you live in that state, and then pass the background checks of that state. (There are loopholes, which could be closed.)
So if a state's controls prevent a mass shooter living in that state from buying guns, those controls will effectively prevent him from legally the guns to use in his massacre.
And if the state's controls do allow the mass shooter to buy guns, most likely he'll do his killing in that state.
So I have no doubt that controls can be effective even if they are local.
Yes, there will be the situation where someone buys guns while living in one state and then moves to another state, or where someone lives right on the border between two states, but those are the exception.
The harder issue is: what controls will work?
I don't want a general ban on gun ownership. I've plenty of guns myself.
Maybe we don't need to go there.
How about a tight, strict system of background checks?
First, you have to have a background check at all. 40% of gun sales are done with no background check at all. That statistic is old (1994) but is the best we have, because federal funding for gun violence research was banned for two decades.
Out-of-date gun background check statistic gets new life after Oregon shooting | PunditFact
(In Oregon, for example, there is no background check for gun sales between private parties, including at gun shows and online sales. A couple months ago this loophole was closed by a state law, but enforcement is up to local police/sheriff agencies and many have stated they will not enforce it.
Oregon gun-sale background checks law gets off to rough start | Local | Eugene, Oregon I think the sheriff in Roseburg has said he won't enforce it.)
Second, the background check has to actually restrict the sale. At present, if a check is not processed within the days, the sale may go through. In other words, the local police or other agency doing the check has to "deny" within three days, or the sale is allowed by default.
DELAYED OR DENIED FOR A FIREARM’S PURCHASE? | Oregon Firearms Federation The Charleston killer got his gun this way - his application was flagged, but the negative information wasn't confirmed in time so he got his gun by default.
Third, the background check and the underlying data reporting has to be effective. The NICS background check uses databases that, in theory, show if someone is a felon, has been involuntarily committed to a mental institution, is subject to a restraining order, or has been adjudicated to be a danger (that would be due to mental illness). I believe there are major "holes" in this system. Some states refuse to submit data to the databases, others don't fund the effort, others simply don't do a good job. The Virginia Tech shooter got his gun this way - he was involuntarily committed, then ordered to undergo outpatient treatment, yet he was never placed on the state's database. And it wouldn't flag someone who was voluntarily committed to a psych hospital, or was a psych outpatient, or had a criminal record not amounting to felony, etc. I suspect the Roseburg shooter will be found to have gotten his guns this way - his various psych treatments, including the inpatient treatment in another state, never rose to a reportable level.
What to do?
- Well, as stated, I'm not in favour of a general ban on gun ownership or on particular types of guns.
- I'd like to see the restrictions on gun purchases tightened to exclude persons who are receiving outpatient mental health treatment involving prescription medication or who have voluntarily received inpatient mental health treatment (including treatment within the last several years), as well as persons who have committed certain misdemeanor crimes.
- I'd like to see medical privacy rules (HIPAA) modified to permit the necessary reporting, and for that reporting to be mandatory by doctors, family members, social care organizations, police.
- I'd like to see these background checks applied to all gun transfers, no exceptions, with no "pass by default after 3 days" (I do think a check should be passed by default if it isn't denied after some longer period, like a few weeks. FYI, most checks are passed in minutes.)
- I'd like to see my state strictly enforcing those requirements, and forcing local police and sheriffs to do so, with the necessary funding provided. If you don't want your state to do so, that's your call.
- I'd like to see CCW permitted in colleges, and by teachers in all schools. (I think private businesses should be able to prohibit CCW, because no-one has to patronize a particular restaurant or theatre or work at a specific job. But you don't have so much choice about attending school.)
- I'd like to see body armor banned, other than for law enforcement/military.