Much of New World is about a succession battle after the don of the Goldmoon syndicate is killed. But do we know who actually killed him? Who's the guy in the car that pulls up next to his?
It's never explained in the film, but I would suspect there are two possibilities:
Ultimately though, there's no right answer - just speculation!
I just re-watched this movie and on second viewing I believe the director does reveal who killed the don.
When Chief Kang stops Jung in the airport he makes a comment that Jung was eliminating the don's guys by accusing them of being moles (ie. the opening scene where a "rat" is killed), and that the next step was killing the don so he could get the throne.
Just watch this scene, the way Chief Kang accuses him he's dead serious. And the way Jung responds, the director first does a shot of Jung being speechless, then after Kang says "Right?", Jung finally brushes it off.