Not to get too graphic, but a single 200 yard shot of a small, moving target from an elevated position…
That’s not some guy that got angry and bought a gun at Walmart last week.

That’s someone who has sighted in a rifle, loads his own ammo so that he knows the grain #, knows how relative weather conditions will factor in, etc.

That’s a miss for 99.9% of people but the assassin only had to shoot once.

Plus he (presumably a male) had a spot picked out and clear escape as he is still at large.

And let’s not pretend like shooting people is easy. I’ve shot deer and it’s extremely hard to stay calm. I can’t imagine the gravity of aiming at a human being.