to the wave of shooting sprees in this country: First, you take away the guns. No private citizen needs assault weapons. Most don't need handguns. Ban the former, license the hell out of the latter. Also hunting rifles. Make it a big pain in the ass to buy a gun -- miles of red tape, reams of forms to fill out, background checks, the works.
The same day that Adam Lanza went nuts at Sandy Hook Elementary School, a nut armed with a knife went into a school in China and started stabbing people. I forget how many kids were wounded, but nobody died. He didn't have a gun because it's against the law in China for a private citizen to own one. The Australian government instituted bans on certain types of guns in 1996, after the Port Arthur Massacre. It hasn't had a similar incident since, and gun homicides are down.
So how do you stop mass killings? You take away the means.
Then you start working on the causes.