The Don could have been reading the newspapers, had the papers read to him, picked up on discussions about the McCluskey-Sollozzo murders from his soldiers assigned to guard him at the hospital or even had a quick visit from Clemenza ("You won't see McCluskey no more")
Anyone operating at the Don's level would not be too concerned with the details of who actually carried out a piece of work, especially while they are recuperating from multiple gunshot wounds. Also if any of Vito's subordinates had earlier confirmed that that the Family did the job on the Turk and the cop, they probably would have been prudent enough to let Vito's personal family (Tom and Sonny) discuss Michael's role.
Why be the bearer of bad news if you don't have to be..
"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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