I doubt gun laws have much to do with it.  Plenty of guns available in big cities as crime statistics would indicate.

Mental illness levels are probably higher in inner cities.

I suspect it comes down to the attention a potentially violent person gets.

In the city, they end up in jail or somewhere quicker.  In the suburbs, maybe not so much. "Excitable boy they all said".

They interviewed several students and teachers who were not at all surprised that this kid shot up the school.  He was expelled for erratic, threatening behavior. The FBI was tipped off a year in advance.

My question is, with all this taken into account, how was this kid able to get armed and actually manage to get close to the school with a weapon.  I sincerely doubt that would have happened in an inner city.