No war is ever kind, but civil wars are the very cruelest of conflicts. The fighting in Syria, as Bashar Assad struggles to survive against a rising tide of anger and insurrection, is no exception. Loyalist troops and airmen have shelled and bombed and strafed civilian areas in an attempt to cow the population into submission.

The effect has been almost entirely the opposite. Survivors of these bombardments who did not join the flow of refugees across the frontiers into Turkey, Lebanon, Jordan or Iraq, or who fled elsewhere inside the country, have turned in their fury to join the rebels. Each massacre by the dreaded Shabiha militia enrages every decent Syrian and, moreover, swells the ranks of the rebels. In addition, these crimes against humanity, tarnish and discredit yet further what little is left of Bashar Assad’s reputation.

Few have doubted, but most have not been prepared to admit, that in this vicious conflict, the Free Syrian Army has, on occasions at least, also been dealing out summary justice to captured Assad loyalists. That has been the tragic nature of civil wars, throughout the ages.

However, in this day of the ubiquitous camera phone, when photographic evidence of the brutal executions of Assad’s supporters is posted on the Internet, the impact is inevitably profound. However unsurprising this act may be, it will shock those around the world, who naively imagined that the insurgents represented all that was decent and good in Syria.

Amnesty International and Human Rights Watch have lead the cry of condemnation for what they rightly characterize as a “war crime”. These two organizations have been zealous enough in pointing the accusing finger at the terrible crimes of Assad loyalists. It is quite right that they should be no less focused when they discover that “ the good guys” are behaving, on one documented occasion at least, with similar savagery.

The problem, of course, is that it does not just end there. In the same way that the opposition’s failure to agree to work together on anything other than the overthrow of Assad has been exploited by Damascus, the video of this brutal execution of regime supporters, including, it is alleged, a leader of the hated Shabiha, plays right into the government’s hands.

Along with his still supportive Russian allies, Assad can now refer to the pictures and claim that these are the sort of thuggish, bloodthirsty and out-of-control terrorists that he is combating, and from whom he is trying to protect the majority of Syrians.

Specious nonsense it may be, but it may seem reasonable to some around the world who are watching Syria and are appalled at the rebels’ actions.

The best way for the Free Syrian Army and the opposition’s political leadership to overcome Assad’s counter-propaganda, will be to arrest and try the rebels, who are clearly seen in the film, organizing and carrying out the murder of these men.

It will not be an easy move, but if the rebels wish to prove that they are truly different from the Assad dictatorship, then they must be seen to punish the men responsible for these extra-judicial killings. Otherwise they may seem no better than the ruthless dictatorship they are fighting to end.