The primary target of any such attack is, of course, our sense of safety, which is to say our trust in the world around us, its people and spaces. The aim is to disrupt our sense of belonging and familiarity and to replace it with paranoia and dread; to challenge our ability to confidently navigate a world we once knew, but which has been defaced in an instant. For inasmuch as we live most of our lives believing ourselves somehow exempt from sudden violence, trust is what’s lost when an horrific event forces it to vacate our hearts, and allows fear to nest in its place.
— written, some time ago, in response to the Boston Marathon bombings, but just as true today, unfortunately. Be well, Ottawa.
andrew (g) forbes 
I agree that mistrust and paranoia are our natural instincts in cases like these, but I believe it’s possible to move beyond those feelings and question what forces prompted the shooter to turn to violence. Once we can do that, I hope we can act consciously against those forces in the spirit of social justice and solidarity with fellow citizens.