Shootings like this are most often domestic or gang related (i.e. - target a specific person and shoot anyone else who happens to be in the way)
Three of the four killed were women. Was it a female gang then? Or was the perp a spectacularly bad shot who could nevertheless score several direct kills against these 'collateral' female targets?
Or maybe he was just targeting whoever happened to be in front of him?
Happened by the make up department. Plus something going on in downtown Seattle.
We will probably find out soon what this was about. Until then, all we have is speculation.