On Friday morning, officers also responded to another "communicated threat" at Noblesville High School, but Jowitt said police believed that's nothing beyond a threat.
Science teacher Jason Seaman tackled a student after he opened fire on his classmates.
Jason Seaman, 29, is a "hero" who tackled the unnamed suspect, according to a boy who was in the class and spoke to CNN affiliates WRTV and WXIN.
He said his brother was a defensive end for Southern Illinois University's football team and had never been a person to run away.
According to WTTV-TV (Indianapolis), several students described how Mr. Seaman rushed into action when the shooter opened fire.
Seaman, a seventh-grade science teacher and football coach, was shot three in his abdomen, hip and forearm, his mother, Kristi Hubly Seaman wrote on Facebook. The person in police custody is a male student now enrolled at the middle school.
The incident was the latest in a rash of school shootings that has plagued the United States and sparked a student-led movement to change gun laws.
Hours after the shooting, law enforcement agents sealed off part of an upscale neighbourhood in Noblesville but weren't commenting on whether the suspect lived there.
A student who wished to not be identified told WXIN he was in the classroom and sitting near a student who was shot. A male student asked to be excused from science class, and left the room, and when he returned, he was holding two handguns, and began shooting.
Jowitt said that the school employs a full-time school resource officer, but does not know if he was involved in the shooting.
One week ago, a deadly school shooting in Texas killed 10 students and staff at Santa Fe High School.
A student, Ella Whistler, 13, was critically injured in the shooting. "If it werent for him, more of us would have been injured for sure".
When asked to elaborate on his praise of the response, Indiana State Police Superintendent Doug Carter said: "Wait 'til one day we can tell you that story". You are too young. The teacher yelled at the students to call 911 and run out of the building. "When the safety of the kids is at hand, it's not surprising to me that he was going to do what he had to do".
Indiana Governor Eric Holcomb, flying back from Europe, said in a statement that he was monitoring the situation.
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