The historian Christian Ingrao notes an attempt was made to make the shootings a collective act without individual responsibility. Framing the shootings in this way was not psychologically sufficient for every perpetrator to feel absolved of guilt.[116] Browning notes three categories of potential perpetrators: those who were eager to participate right from the start, those who participated in spite of moral qualms because they were ordered to do so, and a significant minority who refused to take part.[117] A few men spontaneously became excessively brutal in their killing methods and their zeal for the task.