The execution must be “outside the camp,” but how far outside? Should we compare it to the law of bulls brought for communal error, about which it is also stated “outside the camp,” and there it means outside the farthest of the three camps, or to forbidden sacrifice “outside the camp,” where “outside” means only outside one camp, the Temple proper?
There are four points of commonality between execution and the law of bulls: removal, outside the camp, preparation (both prepare for something), and atonement (both atone). There are also four points of commonality with the forbidden sacrifices: they apply to a person, a sinner, a life is being taken, and sacrificial disqualification does not apply.
However, we should rather compare those laws that prepare for something, thus execution is compared to the law of bulls, and the place of execution is removed three camps from the courthouse.
Art: Eugene Fromentin - Arab Encampment in the Atlas Mountains