She said the gunman wielded a pistol and a rifle, and had a "completely passive" look on his face when he opened fire.
The sheriff called it a courageous action by the staffer.
"There was so much blood", one student said. About 100 interviews have been conducted so far in the investigation, Knezovick said.
One student has died and at least six people have been shot at a high school near the city of Spokane in the USA state of Washington with a suspect taken into custody. The suspected shooter was in custody, according to the Spokane County Sheriff's Office.
Fifteen-year-old Michael Harper, a friend who described Sharpe as "nice and amusing and weird", told the Associated Press the suspect was obsessed with other school shootings.
The high school, the only one in the district, has an enrollment of 327 students, according to U.S. News. Students ran for cover, and some were led to safety at nearby elementary and middle schools.
Student Michael Harper says the suspect recently warned others that something bad was coming.
Harper also said that the suspect had shared a note with some friends saying that he "was going to do something stupid".
A two-lane road into the community of about 500 people near the Idaho border was clogged with vehicles.
The incident took place at Freeman High School on Wednesday morning.
Moser said her son called her from a classroom after hearing the shots and sounded scared. "I've never heard him like that".
Another junior, William Solsom, said, "You wouldn't really expect something to happen at a school like this".
The three victims were taken to Sacred Heart Hospital after the shooting. Investigators said three other people were hurt and are in stable condition. The lockdown at the school systems that was triggered by the Freeman High School shooting has been lifted.
The prevalence of school shootings in the US has been blamed on the widespread availability of guns.
"Not knowing who is affected is hard", Roecks says.
"My stomach's in tangles at the present time", she said.
Authorities are responding to a shooting at a high school south of Spokane.