The suspected shooter at Arapahoe High School may have been a student seeking revenge over a conflict with a teacher, Arapahoe County Sheriff Grayson Robinson said.
Sheriff Robinson said the identity of the gunman will not be released "until everything is confirmed".
More top news
Watch Hollywood heartthrob Chris Pratt doing a flawless Essex accent after revealing his wife Anna Faris is the reason behind it.
It will be breezy and wet tonight as rain sweeps in from the west, meaning a miserable start to Sunday morning.
BBC Political Editor Nick Robinson has revealed Labour tried to recruit him to be Ed Miliband's spin doctor in the run-up to the election.