[DeadBolt]

The guys are the same and heres how:
Notice the missing helmet. When he kills Mellish he loses his helmet and in the end he says "Upham" and has no helmet on. You can tell by the look Upham gives him. They let him go after he killed Wade and he killed men from his squad again. The way the whole scene is set up. Just because they are wearing different uniforms doesnt mean jack. He got a new one. Its obviously him because of the irony in the story. They let him go only to let him kill again, and Upham finally gets up the courage to kill when he sees him kill Miller. Its obviously the same person.