So this is a outlier only in that someone was equipped and trained to a fairly serious degree. Someone on the order of a squad designated marksman (SDM) is certainly capable of this. The US military has a few thousand active duty personal trained to that level across the several branches, and there are 10's of thousands of veterans. There are also many SWAT and other LEOs and an uncountable number of enthusiasts and serious hunters with sufficient training and weapons.