This is not even comparable to the assassination attempt on Trump, where the guy fired multiple shots and missed. The person who killed Charlie knew what they were doing, aiming at the jugular artery, possibly a professional. The fact that they couldn't even find the person makes no sense. How long is it going to take for someone to escape the roof top and get away with it? Isn't US intelligence so good it can catch people doing crimes from different parts of country and even the world? If they don't catch the person it's because it WAS an inside job..
I've never shot a rifle like that, only a few pistols (a couple of different glocks and a CZ), some shotgun, and a couple of AK variants with and without optics. The range I was shooting at was maybe like 70 meters at the furthest so didn't really think about bullet drop much. Guns aren't super popular here.