The suspect is in custody at the Spokane County jail.
"We need to figure out what's going on with our society, that our children decide they need to take weapons to deal with the issues they're facing", Knezovich said.
The sheriff says a student approached the shooter and attempted to block him before he was shot and killed.
The shooting happened around 10 a.m. Wednesday when a student, whom numerous students identified as Caleb Sharpe, opened fire at the school. A custodian stopped the shooter, a heroic action the sheriff said prevented more bloodshed.
The three wounded students were transported to a hospital and are expected to survive, authorities said.
Knezovich said the shooter's first gun jammed before he pulled out the second one.
The shooting suspect is a student at the school, which is a public school for emotionally disturbed students in grades 6-12.
"It's been unbelievable, within probably 15-20 minutes of hearing about it, I'd already received a phone call, I'd already received a text message saying that their school is OK", she said.
The "bullied" 15-year-old boy accused of killing a student in a mass school shooting posted violent gun-fight videos on YouTube. He fired more rounds down a hallway, hitting the three female students.
The shooter had many friends and wasn't bullied, Harper said, calling him "nice and amusing and weird" and a huge fan of the TV show Breaking Bad.
Colorado law states that staff members can carry concealed weapons in schools if they have a permit and are designated as a security officer. The victims also were not named.
The shooting was reported at Freeman High School in Rockford on Wednesday.
This is a real close-knit community, he said.
A two-lane highway into the town of about 500 people near the Idaho border was clogged as anxious parents sped to the school. Some people abandoned their cars on the street to make it to their children.
Students wait on lockdown inside Freeman Elementary School in Washington State?s Spokane County after a shooting at the nearby Freeman High School.
He called me and said, Mom, there are gunshots.
"I heard this really loud noise, I thought someone had dropped something super heavy", Freeman junior Marcus Morphy told CNN affiliate KAYU-TV. They were in stable condition.
The Associated Press doesn't typically name juvenile suspects but is doing so because of the severity of the accusations and because Sharpe's name was released in publicly available documents and was widely used in local media.