I'm clearly an outsider to that topic coming from a country with relativly strict gun control.
But hows the overall statistic about that?. Using single events, to emotionalize a debate, won't help in a constructive discussion.
Mass shootings and amok runs are something completely different than criminals using a gun. The whole motive for someone to snap and kill others is different to the criminal mind and motivation.
How many people kill others by accident?
How many people killed other with guns who wouldn't pass the background check?
Where do the criminals get their guns from? (theft?, bought through some dark channels?)
What are the social and economic factors of people abusing guns?
This is part of the problem. Mass shootings account for an incredibly small number of deaths every year but they are emotional effective for passing new laws. Most gun murders (including mass shootings) are committed by gang members and drug dealers. When people talk about this in the media they leave this part out and make claims like "All mass shooters have these things in common" (which doesn't account for the gang members and drug dealers) but them point at total numbers of mass shootings by the US definition (which do account for gang members and drug dealers). This way it sounds like all instances have a common problem of legal gun ownership, mostly young white men, certain political beliefs and anger toward a specific group of people (usually based on race or gender). The truth is, most homicides of all kinds, including mass shootings, are caused by basic human drives that we all feel: greed, jealousy, anger, etc. except by people lacking the proper tools to stop themselves from acting out on them.
About accidents 169,936 in all, 486 from firearms. Training might be enough to end 90% of these without infringing on people's rights.
When talking about the kind of shooting that most of us think of as a mass shooting, they seem to all pass a background check. One last year shouldn't have but we had different agencies not properly communicating information and the ones that are underage use their parents weapons, who do pass a background check. I wouldn't take this to mean that background checks aren't effective though because we don't know how many people who would have done these things couldn't because of them. I think it just means that current laws around background checks are as effective as they can be. All they are really doing is making sure that you aren't already a known threat (i.e. convicted felon).
The media will tell you that most criminals guns are purchased legally and this is true, just not typically by them. Criminals without records will buy them for their friends, they will steal them from people who purchased them legally and they will buy them off the street but even most of these were legally purchased at one point.
As far as social and economic factors, everyone already knows this one. Poor, single parent home, from an area with failing schools and living in areas where this activity gains respect and protection from others. THIS is one of the things that my country continually fails at.
But, In the end you are almost as likely to be killed by a fall than by a gun (37,587 vs. 39,773) and around 60% of gun deaths are suicide with only around 800 are from all mass shootings (again, mostly run of the mill criminals). You are almost 4 times as likely to be killed by the flu than to be murdered by a gun and more likely to be beaten to death with a hammer than killed by an AR-15. The only two statistics tracked by the CDC that have a lower death rate that mass shootings are legal intervention and accidentally shooting yourself.