We are on this planet since... 4 hours at most. What those three attacked, was not us, but what we currently still represent - A beneficiary of the empire. That is to say, they also feel that the empire is flawed, if they act against one as us in such a way. Torturing him, for being a victim of his own lot?
Well, I actually have nothing against us being so efficiently coldblooded, not in the least, no. Neither would it be unjustified in this context, but still, as food for thought.
Either way, I would be for a longer interrogation. Let him drop the weapon, and put those chains on him at lazpoint.
We will be able to ask him "suspicious" questions, and will have an easy way of dealing with the aftermath of this action.
As for suspicious? Where are the local Arbites, their equipment and patrols or interests. Is there one of "our" temples ("forging" our way into there, or plundering it for materials?), any rumours of any heretics, the current mood of the populace, their grievances, anything of that sort that we could put to good use. Then there is also the question of where to get our materials - any scrapyards around, or maybe straight from the mines?
About the mines, since we are undoubtedly more efficient in our ways than those of our old, misguided order, it would be a piece of cake to officialy take over one of these mines with a forged identity, give the empire the expected amount of resources, and pocket the vast differences. The later would pile up like interest... well, just an idea of what we could do.