The plan was to either capture or kill large numbers of the Victorian police. The prime targets were the Aboriginal police-trackers. The idea was to lure the police to Glenrowan. In order for this to happen they needed to show themselves with the guarantee that once they had done so, the police were sure to follow.
Ned knew that the trackers and police would come looking for him. It had been many months since he and the boys had shown themselves. It was known that Aaron had four policemen staying with him in his hut. Killing Aaron would surely have the police in hot pursuit.
Most historians believe that Aaron's execution was part of the plan, however another theory is that Aaron was only meant to be frightened and Ned was unaware that Aaron had been killed by Joe.
Either way, the 'spy' as Aaron was known, was executed, unfortunately the police were so frightened that they did not leave the hut until many hours later.
It is understandable that the police should be so scared, after all they did not know how many outlaws were involved and they were prime targets inside the well-lit hut.
Joe and Dan performed this 'execution' via the bailing up of a local German market gardener named Anton Wicks. Anton often got lost and would ask Aaron to show him the way home. This time however he was being forced to ask for directions at gunpoint, "it is Anton, I have lost my vay". Aaron thought nothing odd about this and opened his rear door. Aaron peered out into the darkness and said (believing he was talking to Wicks) "Do you see that sapling over there", it was to be a joke, instead Aaron received a fatal wound. Joe fired two shots...