In the wake of the San Bernardino shootings, we are again obsessing over what drives people to commit horrifying acts of mass murder, and how we can identify these killers before they strike.

Against a background of political candidates ranting provocatively about declaring war and closing borders comes a thoughtful and, in a very different way, also provocative essay by Mary Ellen O’Toole, PhD, the editor-in-chief of Violence and Gender, the journal founded by the Avielle Foundation. Avielle, you may recall, was the 6-year-old daughter of Jeremy Richman and Jennifer Hensel who was one of the 20 children murdered at Sandy Hook Elementary School 3 years ago.

In her article, Dr. O’Toole takes on some of the misconceptions about what she calls “mission-oriented shooters,” those whose goal is to kill as many people as possible. She notes that these shootings are anything but impulsive. “The planning is strategic, complex, detailed, and sufficiently secretive to minimize the risk of being detected and maximize the chances for success, ” she writes.

While it’s appalling to think of this kind of cold-blooded preparation, it also means that there are many points in which planning behaviors might be observed, by parents, fellow students, coworkers, retailers, and innumerable others who come in contact with them while they prepare for their mission.

And even before the planning, she notes, there is a stage of evolution in the shooter’s personality and habits, development over time of anger, resentments, enmities, obsession with weapons, devotion to extremism. This, too, she writes, “provides first observers with opportunities to intervene as long as this preplanning behavior is not ignored, rationalized, or explained away as something expected, typical, or ordinary.”

Dr. O’Toole is an FBI profiler, so identifying risk factors is her specialty. What’s provocative here is the notion that it’s not just a matter for professionals. All of us are part of communities that, by closer observation of those around us, could do much more to identify red flags. She wants all of us to be “first responders,” willing to step up and call attention to signs that someone is in distress or a danger to others.

It’s scary—the notion of friends and neighbors being on the alert for danger signs from each other. But a tragedy like the one that happened in San Bernardino or in Newtown is long in developing, and we need to get better at recognizing and responding to signs of trouble. Close attention to behavior may offer more opportunity than drones and closed borders to keep weapons out of the hands of people who intend to do great harm.