One person could NOT have done the Lewiston, Maine shootings in 12 minutes!

I ran some real world numbers concerning the Lewiston, Maine shootings and there is no way that one shooter could have done this. My model is based on 3 minutes inside each building, plus two minutes each time the hypothetical shooter went from parking lot to building and then another two minutes back to his vehicle. Travel would have certainly been slowed by traffic lights and other vehicles.