Proof reference link, also with pictures of each mass shooter on one page:
https://mass-shootings.info/index.php
Great information at the link. The information for the two previous years trends the same way as the 2021 data.
The Secret Service did a study on school shootings fairly recently. Probably the biggest common denominator is a broken home.
https://www.secretservice.gov/sites/default/files/2020-04/Protecting_Americas_Schools.pdf
Is that just in 2021?
Bkmk