The novel implies that Luca pulled off the horse thing. Let's not forget that it was Tom who arranged the murders of both Khartoum AND Geary's hooker.  I always thought that it was left hazy as to exactly who had killed the horse? The Don had LOTS of friends and connections. He could have had that arranged by his friends on the West Coast, no?
"When the snows fall and the white winds blow, the lone wolf dies but the pack survives."
Winter is Coming
Now this is the Law of the Jungle—as old and as true as the sky; And the wolf that shall keep it may prosper, but the wolf that shall break it must die.
As the creeper that girdles the tree-trunk, the Law runneth forward and back; For the strength of the Pack is the Wolf, and the strength of the Wolf is the Pack.
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