Tom called Carlo a few minutes after learning about Sonny's death before even telling anyone else in the family.

What he did in that conversation was to let Carlo know that he was, as the novel says, "a hair away from death." Yet he did so without uttering a threat to Carlo. Instead he almost made Carlo feel that he would protect him and make things straight with the others on his behalf. He got the message across to Carlo and in a sense took control over Carlo, so as to keep him in check.