The skull on the mantle of 221B is that of Carl Powers. When Sherlock says, “Friend of mine. When I say friend…” to John it’s because he can’t think of another word to use. Friend. Carl Powers, Sherlock’s first case, his first real case. It gave him a distraction. It eased the boredom. So, to Sherlock’s mind, Carl Powers was a friend, his first friend in fact.