At certain ranges even an amateur could do that to a stationary target with iron sights ....especially if they are not looking for a 'spectacular' shot like a head shot but just looking for a hit somehwere in the victim's upper torso! Toss in a telescopic sight and even head shots become possible.
Now, let's say this perp has had the rifle for some time! That means he is used to using a rifle ...maybe for hunting, or maybe he was ex-military! Whatever! In essence he is a chap who knows how to handle a rifle. At least marginally. And when it comes to sniping with a sighted scoped rifle all he needs is marginal esperience in shooting!
The only great skill involved in this case is the ease at which he has managed to evade capture. Otherwise his shooting is nothing phenomenal.
And when we are talking 200 yards with a 'sniper rifle' then you have to wonder ......should this person even be called a sniper or just a psycho-perp with a rifle? When i think 'sniper' i think of Serbs and Croats perched in bombed out buildings shooting mobile enemy personel that are aware of the presence of snipers and are hence taking adequate care, and firing targets at distances approaching a mile with only a split second for aiming and firing, not to mention factoring things like wind shear and gravity! That is a sniper. Not some guy 200 yards away shooting innocent people who are stationary and in vulnerable situations like filling gas, and then leaving tarot cards saying he is God! Again the only real skill i see in this perp is his ability to melt away. and maybe that is just due to luck!
As far as the inferior weapons of an armed public, the odds have it that sooner or later someone will got a bead on the b------ from behind cover. Then others will join. That will be the grave for that clown. It will be tough to fight an army of mad, good people.