I had written about this in past years, but I thought I'd update it to reflect the El Paso incident from last week. According to the El Paso Police Department (see also CNN [Andy Rose]), a confrontation between two groups of teenagers at a mall "escalated into a physical fight" and then into a 16-year-old fatally shooting a member of the other group and seriously wounding another member, as well as injuring a member of his own group. Then,
As soon as the shooting ended, the 16-year-old suspect began to run and was pointing the gun towards the direction of bystanders, including 32-year-old Emanuel Duran, a Licensed to Carry Holder. As the suspect ran towards Duran and bystanders, Duran drew his handgun and shot the suspect.
At that time, one off-duty El Paso Police Officer arrived at the area of the shooting and together with Duran rendered aid to the 16-year old suspect and the others that were injured. Investigators found that there were at least two other legally armed citizens in the area of where the shooting took place, but were not involved.
Now in this case, the suspect didn't seem to have planned a mass shooting; he seems to have had a beef with the other teenagers. On the other hand, he appears to have been pointing his gun towards the bystanders, so it's hard to know what would have happened. And something similar could easily have happened with an intended mass shooting as well; for an incident like that from last year, see this WCHS-TV story:
