In the case of the horrible events at Sandy Hook, it took the monopolist government protection personnel at least 7 minutes to respond to calls for help. Those professionals did not have to discharge their weapons because the killing and wounding had already been accomplished to the satisfaction of the murderer.
Had the murderer been only able to bring a baseball bat, he would have just killed maybe half as many children.
It is true that when seconds count, police help is only minutes away. A recent survey of almost 100 mass shooting events showed that when it was terminated by police on average 14 people were murdered and when it was terminated by someone on site, less than 4 people were murdered. Moreover, with a single exception, these mass murders took place in gun-free zones.
Given the left’s reaction to the suggestion that it is prudent to have at least one person at a school who is armed, it is clear that all this gun-control feeding frenzy is far more targeted (to borrow a word) at grabbing guns than to increasing the safety of school children.
If he'd been a follower of Bill Ayres, he could have brought bombs, and killed a whole bunch more.