Ok, let's get this straightened out:
1) I said yesterday that I suspected Orange for scum.
2) I announced that I would be investigating him purposely to set up for today's test.
3) I only had time to glance at my PM at the time. I noticed the passive being killproof, but at the time I wanted to execute my test as quickly as possible before others could direct the spotlight.
4) As I said, I believe that if Orange were hostile with a killing ability, he would think I was telling the truth when I said I discovered it and thus create an alibi for having it rather than denying its existence.
5) I'm no thief, Orange still has his passive and he's said as much.
6) I have several methods of determining a player's alignment through my ability. As Cat5 said, catching a player in a lie. Another method is using deduction to figure if an alignment needs whatever ability the player has, just as you're doing now. For example, why would a scum alignment need a killproof passive? Scum wouldn't, but third party might to protect themselves from scum, which is another reason I preferred to continue pushing my bluff as a backup to the passive ability.