In U.S. mass-shootings since 1992, when the first person to shoot back is an on-duty police officer or SWAT team member, the average number of dead is 12.4... but when the first to shoot back is ANYONE else (including off-duty police), the average number of dead is 4.8...
Haven’t seen those numbers before. Do you rrmember the source?
It needs more play on the Internet:
http://gunwatch.blogspot.com/2015/07/average-mass-shooting-stopped-by-police.html