When I made my post you quoted I was going to list all of the mass shootings (three or more people) in the last several decades in America. However, they are quite numerous, and I was not motivated enough to organize the data and provide the list. I can offer you my word that the vast majority of the shootings were in gun free zones. Specifically, most were schools. There were also places like the Amish school shooting in 2006, where guns may not have been technically banned (I don't know), but where the gunman did not face armed opposition due to the particular community's culture of being weaponless.

I am still unmotivated to organize the data and provide the list here. If somebody else wants to take the ball and run with it, then I'm sure some people will appreciate the effort.

Important point, we may not need to know the actual mindsets of the madmen. We can make educated guesses from the stats. It's common practice to analyze historical data to predict the future. For example, if you were to guess the more likely place a mad gunman would strike of the following two locations, where would you guess: (1) a crowded high school auditorium in Colorado or (2) a crowded police station in Colorado? What would be your reasoning for making your guess?