No clue about the scratch...but if history tells us anything you're probably going to have at least one more death, if not two.
Having more than two clowns in less than 200 gallons is incredibly dangerous in captivity, and will often end with the dominant female and male killing the others, and sometimes even one or both of the pair ends up dead.
It could be any number of things that caused the death of your fish. Did you QT these fish before adding them to your display tank? Without knowing anything more about your fish it's tough to say...was it breathing heavily? Did it have any unusual growths on it? Were the eyes cloudy?