Tony Didn't Kill Ralph Over the Horse

A man is on his kitchen floor with his hairpiece knocked loose, and the boss of North Jersey is sitting on his chest, choking him to death with both hands. There is bug spray on the linoleum. There is a kettle. Ten minutes earlier these two men were eating breakfast. Nobody in the room, including the man doing the killing, can tell you exactly why this is happening. That is not a gap in the writing. That is the writing. By the end of this, you are going to understand that The Sopranos gives you three complete, airtight, mutually exclusive reasons for Ralph Cifaretto's death, and that the show does this on purpose, and that the reason you pick says... What did Tony Soprano actually kill Ralph Cifaretto for, given that the show deliberately refuses to confirm the horse, the insurance money, or the twenty years of accumulated contempt?