I'm not interested in driving off the player. He's a fine guy, but he does run a little "kill them and take their stuff." My goal is to teach him that this has severe consequences when done lightly.
Now, my problem is compounded because... the other players are backing him up on this. The theme seems to be that since the Verditious were on trial, that it was less-bad than if they were just out of the covenant. (And they think that the Verditious wouldn't press the issue because they will be in more trouble than Gaius.) And they certainly seem to be suggesting OOC that they don't think it should be a marchable offense.
Which astounds me and makes me question if I want to keep on in this group.
At the moment, I'm leaning towards letting Tribunal sort it out. The Verditious will press the issue, after having secured alliances. They will be calling for him to be Marched. The players don't have any political ties or clout yet (in fact, the little political bonding they had done was with their former friends, the Verditious), so they will have to build a power base right quick if they want to defend the PC. Of course, they will have the option of throwing him to the wolves if not.
Since I know it will be asked: The Verditious sold an automaton to a nobel through their vendor. It was a toy-- a doll. The noble's daughter showed it to a clergiman who used it as evidence that they were binding demon familiars.
And also, since it came up, I've been talking with the players, and one who knows the group better than me (I'm the johnny-come-lately), believes that the player in question knew his life was in danger when the Verditious came back asking questions... and worked out that the fact that since he had TWO fili and an apparent age in the 40s that he might be a problem. So, I'm inclined to give them an honest chance of saving him... or blowing it and getting him Marched. It will be curious to see what happens in that event.
Thanks for all the advice, and above all for reassuring me that this was a pretty wrong thing to have done. When every one else at the table is all "What's the big deal?" and "Well, I woudn't have done it, but I see where he's coming from" you can start to wonder.