As we waited for Oscar Pistorius to be freed from prison on parole last week, many among us felt that he had not served enough time for the senseless killing of Reeva Steenkamp. It is difficult to articulate this subtle unease - an intuitive sense that there has been a mistake, a mismatch between crime and punishment. Yet this sense seems to be so widely shared (including, it seems, by the minister of justice, who suspended the parole approval at the eleventh hour) that it can hardly be dismissed as primitive vengeance.

And it isn’t.