The man whose head that Qin Feng kept was someone that he was sure was from the Dark Coalition he had seen on the bounty hunter network.
This ancient warrior, however, was just a small corporation's president. There was not much loot he could get from him. And if he left his corpse lying around, there would be others that would use it against him within the politics of the Human Alliance.
As such, it was best for him to burn his corpse whole.
With that, even if some people suspected him, Qin Feng could just pretend that he did not know about it. Also, no one had solid evidence that he was the one who killed him too—no one knew that this man was that president because he had his face covered behind a mask seconds before his death.
Then, Qin Feng started to move from one cube to another again to kill every single A-tier that challenged him.