From Choc - "Others have compellingly argued that those poor little boys were murdered with a frenzied arc of shots and in a manner which suggests overkill - the sort of overkill that parents who kill their children indulge in."
Frenzied and arc don't go together IMO.
It was either frenzied or arc.
In a frenzied attack I would expect shots all over the head and / or body.
The arc to me indicates a controlled act, and has been referred to months ago on the forum as a more execution style of shooting!
And the term "overkill" can apply to anyone wanting to make sure death was quick and final.