One common thread in the three school shootings below college level that everyone talks about is that in each case the killers were under 21. Harris and Klebold were 17 and 18, Adam Lanza, who stole his gun from his mother, was 20, and Cruz was 19.

The two college shootings (Virginia Tech and Umpqua College) were done by a 22 year old and a 26 year old.

Clearly we are dealing with a new breed of youth much more likely to launch these type of attacks.