If the family disposed of Carlo's body in a landfill, the bottom of the river, or a hidden grave, then how would his death be in the papers??

But, they could have have just dumped Carlo's body in a public street in Barzini's territory (as that would a fitting message to the Barzinni family). The papers could then have written up Carlo's death as mob related. But Connie, could have seen through those reports in the paper, to assume it was her brother that ordered him dead, just as she knew the Communion Day Massacre was by his orders.