Seems like there was one at a Georgia college (Law school maybe) some years ago where someone went to his car and got a gun and killed a potential mass killer.
Something like that happened in 2002 at the Appalachian School of Law in VA. The perp was a middle-aged Nigerian former student.
According to the wikipedia article, there were two different witness accounts as to how the perp was subdued. This is one version:
"According to [Tracy] Bridges: at the first sound of gunfire, he and fellow student Mikael Gross, unbeknownst to each other, ran to their vehicles to retrieve their personally-owned firearms[6] placed in their glove compartments. Mikael Gross, a police officer from Grifton, North Carolina retrieved a 9 mm pistol and body armor.[7] Bridges, a county sheriff's deputy from Asheville, North Carolina[8] retrieved his .357 Magnum pistol from beneath the driver's seat of his Chevrolet Tahoe.[9] Bridges and Gross approached Odighizuwa from different angles, with Bridges yelling at Odighizuwa to drop his gun.[10] Odighizuwa then dropped his firearm and was subdued by several other unarmed students, including Ted Besen and Todd Ross.
Once guns were merely a tool and were seen as such. Today guns represent power. It’s that simple.