A major part of this investigation will be sorting through the photographs and video that police have requested from the public. The deluge may test the capacity of law enforcement to catalog and analyze so much material, but crucial clues are likely hiding in the digital files of marathon-goers who were unfortunate enough to be near Monday’s explosions.

One good sign is that there don’t appear to be any major turf battles going on among local, state and federal authorities involved in the investigation. The FBI quickly took leadership, thanks to protocols put in place in the late 1990s and after 9/11 that set jurisdiction for different types of incidents. This allows other agencies (at all levels of government) to fall into line and know their respective roles. When I was on the Boston force, by contrast, all sorts of incidents—for example, a plane running off the runway at Logan Airport and into the harbor—would be followed by unproductive turf battles between city and state police.

The past few days have also vindicated the sort of heightened preparedness emphasized by security and health officials since 9/11. Controlling crowds and directing traffic remain priorities for Boston police on the day of the marathon, but they have also drilled to prepare for much more. The police tent by the finish line has gotten bigger over the years. Whereas it was once equipped mainly to deal with exhausted and dehydrated runners, it now hosts a wide range of personnel ready to activate various contingency plans, including responding to a terrorist attack—how to deploy emergency-medical technicians, where to arrange the ingress and egress of ambulances, etc. Then there was the senior doctor from Massachusetts General Hospital who noted that his team was prepared for the gruesome injuries they encountered because they received training recently from Israeli doctors experienced with terrorist bombings.