[two23]

"Could someone very well trained pull this off on foot? Just wondering

I may be proved wrong, but I believe the person(s) probably have some background in firearms/training. Either LE, x-military or just hunting/range targeting..anything is possible at this point cause we don't know much.

[BlessingInDisguise]

Ya right, you don't need training. You put the bullet in, you aim and pull the trigger. I'm sure whoever this is, has probably got a considerable amount of range time though.