“Possible shots fired.”

This week’s response to the dramatic events in Ottawa began Wednesday at 9:52 a.m. with an all-too-familiar 911 call. It was followed, within a minute, by a dispatcher’s startling update: “We may have multiple patients. One soldier has been hit.”

That ignited an unprecedented emergency response that flooded downtown Ottawa with more than 400 police officers, paramedics, hostage negotiators, tactical officers and incident commanders. Reports followed of gunmen on Parliament Hill, in the Rideau Centre, on top of the Château Laurier. Confusion — and terror — reigned for much of the day as politicians, civil servants, shopkeepers and students locked their doors against an unknown threat.

Three days later, we know, of course, that the mayhem was the work of a lone gunman, and that the threat he posed was extinguished seven minutes after his cold-blooded slaying of Cpl. Nathan Cirillo, who was shot twice in the back…