Mark, along with other students and witnesses, told investigators that there were shooters on the roof. Mark made public statements to this effect for several years after the massacre. However, the “official” Jefferson County Investigation claims that the man on the roof was an air conditioning maintenance man. Nearly ten years after the massacre a video tape was obtained that was filmed live during the shooting revealing that not only was Jeffco lying about there being no rooftop shooters, there was, in fact a whole SWAT team on the roof shooting blindly into the building. ”Covering fire” it was referred to if you dig into the 40,000 + pages that came out in the years after the official 10,000 pages were released. See for yourself: http://columbinefamilyrequest.org/cases-being-investigated/rooftop-shooter/
