After every major event--whether it is a mass shooting, a plane crash, a natural disaster, or a terrorism event--there is a set order for things. First response, then recovery, of course there will be investigations conducted by various entities (depending on the event this could include local law enforcement, hospitals that were involved, the FBI, NTSB, CDC, FEMA, etc), followed by a gathering of data and information, and concluding with a quality improvement process that looks at what happened, why it happened, how the event could be prevented or mitigated, and improvements that could be made to future responses. These "hotwashes" and "after action reviews" as they are called, are a tried and true way to learn and improve from each event. Of all the things I miss about my previous work, being a part of these types of review processes is probably what I miss the most.
When you gather responders together after an event it can be both cathartic (oddly enough my first thought when I heard the news about yesterday's shooting was 'I hope the disaster mental health folks show up on scene ASAP', yet one lesson learned from previous disasters) and enlightening (there is ALWAYS something new to learn from each event. Always.). The after action review process allows everyone who responded to an event (or in the case of a large event there will be representatives from each responding agency) to gather together and discuss what happened, discussed what worked with their response, and discuss things that could have been done better. The "lessons learned" then impact everything from how emergency responders are dispatched to how on-scene command works to better ways to stage for the incident to tactical applications, etc.
This is why law enforcement response has changed drastically when it comes to school shooting incidents (due to lessons learned from Columbine), why the New York City hospitals were able to evacuate seemingly effortlessly during Hurricane Sandy (due to lessons learned from Hurricane Katrina), and why processing bodies and dealing with family members of the dead is now a streamlined process (due to lessons learned from 9/11, Oklahoma City bombing, the tsunami, et al). All of these improvements have been built on what worked and what didn't work during past disasters.
And now for some light reading: