Let's say your boss didn't know the whole story about a fight in your workplace. There was a fight that happened between your 2 co-workers and you broke up the fight. You have successfully stopped it. A few hours after that, your boss, who just clocked in, ignorantly asked you "why did you fight?" Then you annoyingly answered it by:
Seriously?! I AM the one who was breaking up the fight.
Seriously?! I WAS the one who was breaking up the fight.
This question pertains to expression-verb tense problem, what is correct?