Rat Breath

This morning all dogs went into the back yard.  Greta stood on the porch barking at birds; Liesl roamed looking for bugs in the grass;  Oscar had his ball clenched in his teeth; Fritz roamed the yard looking for food - any food.  This left Bruno who was reclined down the hill in the grass and sunshine.   He was in Heaven - soft grass and warm sun.  What a life.
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This morning we needed a short run into town.  The dogs were moved into the house except Bruno. He chose to lie in the sun and ignore me.  I called time and time again.  Snore.   "Cookie?"  I yelled.  He stirred slightly.  Once again I hollered, "C'mon Bruno, inside, cookie, cookie."  This got him.  
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He rolled to his 4 ample paws and rotated around, as dachshunds must do to turn corners.   Bruno took one step forward then picked up something in the grass.  Right away I recognized it as NOT A BALL.   What was it?  A bird maybe?  I stepped into the house and told my wife to get ready to be grossed out.
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Bruno strolled into the house and I could see.  It was not a bird.  Look at the title of this.  Not a cute little mouse, but a big ole rat.  It had a 6 inch tail and a big fat body.  I told him to put it down. Bruno thought that was wrong, really wrong.  None - I say None - of the other dogs gave Bruno and his treat a second glance.  They could care less.
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With a slow hand, I grabbed Bruno and lifted him straight up and away from the dead rat.   It was a bloody mess.  I picked it up and threw it over the fence.  Then, Bruno got a cookie.  I think he would have rather have the rat.
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The question.  Which one killed the rat?  Bruno, Oscar....?  I have not the slightest.  It doesn't really matter I suppose; the rat is dead; the rat carcass is over the fence; and Bruno had his cookie.