The fundament of genuine Law everywhere is that all men/citizens/people are bound by it and since nobody is above it, similar cases should be treated similar and different cases different. That is jurisdiction filling up the principle of equality for the Law. A criminal who is being prosecuted for a crime and sees that others who have committed the same crime are not, can fight the prosecuters susceptibility to prosecute him on the basis of violating this fundament and therefore undermining the integrity of and the common believe in the Law. A tactic Jacques Verger used in the Klaus Barbie trial. A judge or court can dismiss the prosecuters claim on susceptibility on this basis and only allow the trial to continue after the others are also prosecuted. One can have the opinion this is morally not just of course but this is judicial reality pretty much around the world.