Maybe they were from the night of the murder, but I'm not sure his classmates wouldn't have mentioned seeing them--unless he had them covered up. One of his classmates said he was "quieter" after the murders, but nothing else. I would think if he had bruises and scratches, some might have been on his face or neck, where he couldn't cover them unless he used makeup, and I'm sure someone would have noticed a guy with makeup.
Then again, we heard some of the murdered students had "defensive" wounds, but I guess that could mean stab wounds in the forearms as they tried to shield their faces or something.