>And now seeing this just puts my fear and worry into reality.

We absolutely should not accept things like this happening.

But in terms of managing fear it's useful to keep two things in mind:

1. Road fatalities in Massachusetts are twice as common as homicides; you're more likely to be killed on the way to the mall than once there
2. Homicides in Massachusetts are less than half the national average

And those numbers are looking at homicides overall, which are dominated by situations where there is an existing and known (even if one-sided) conflict between the parties. A bystander being killed is shocking and horrifying, but it is also even less common - the rate of "random" homicides is really very very low in terms of the risks we face when going about our lives.