I've been wondering... the sword/knife that is able to kill angels (the one uriel used) does it belong to Michael or Lucifer? (I cannot seem to remember. I must have missed something)
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Actually, it's not the knife that killed Uriel. It has been mentioned that only an angel is able to kill another angel [as shown by Dean stabbing Cas with Ruby's knife in the first episode of season 4 with Cas feeling no effect]. It is the same as Cas killing his fellow two angels in season 5 with another type of knife. The knife that killed Uriel belonged to no one at all. It could've been Uriel's for all we know.
