Investigators are now working to figure out whether Pierson intended to target specific people in those rooms.
Pierson also inscribed a Latin phrase on the inside of his forearm, which translates to “The Die Has Been Cast.”
The investigator’s report also clarifies what happened during the 80-second attack.
According to the report, Pierson entered the school opening carrying as .12-gage shotgun and wearing 125 rounds of ammunition in bandoliers across his chest and around his waist.
He fired five times with his second shot hitting 17-year-old Claire Davis at point-blank range.
Davis remains in a coma in critical condition at a local hospital.
The attack ended when Pierson shot himself in the library of Friday.