Police say investigators who are trying to determine why a sixth-grade student brought a handgun to her Idaho middle school and wounded three people after opening fire are "looking into" reports claiming she posted a video on social media in the days before the attack. 

Jefferson County Sheriff Steve Anderson made the revelation Thursday during a press conference following the shooting at Rigby Middle School in Rigby earlier that morning.  

"They are aware of that and they are looking into it," Anderson told a reporter after being asked about a video that is purportedly circulating on TikTok. Anderson did not comment on the content of the video.

A police officer walks out of Rigby Middle School following a shooting there on Thursday. (AP)

A police officer walks out of Rigby Middle School following a shooting there on Thursday. (AP)

IDAHO TEACHER DISARMED STUDENT IN SCHOOL SHOOTING, POLICE SAY 

EastIdahoNews.com says it has received "dozens of messages stating she posted a threatening video on social media days before the shooting." 

The shooter is from Idaho Falls, police say, but as of Friday she has not been publicly identified. 

The student pulled the gun out of a backpack before she opened fire, authorities said.   

"During the shooting, a teacher disarmed the student and detained her until law enforcement took her into custody," Anderson said Thursday. "She did take the handgun from the student." 

The student was not in the teacher's class, Anderson added. The shooting started inside a hallway in the school where two people were shot and moved outside the building where the third victim was struck, he added. No motive was disclosed.    

The three victims were shot in their limbs and are expected to survive, officials say. 

Students walk past police tape after the shooting at Rigby Middle School (AP/The Idaho Post-Register)

Students walk past police tape after the shooting at Rigby Middle School (AP/The Idaho Post-Register)

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Police were called to the school around 9:15 a.m. Thursday after students and staff heard gunfire. Multiple law enforcement agencies responded, and students were evacuated to a nearby high school to be reunited with their parents.  

"Me and my classmate were just in class with our teacher — we were doing work — and then all of a sudden, here was a loud noise and then there were two more loud noises. Then there was screaming," 12-year-old Yandel Rodriguez told the Associated Press. "Our teacher went to check it out, and he found blood."  

Yandel’s mom, Adela Rodriguez, said they were OK but "still a little shaky" from the shooting as they left the campus.  

Schools would be closed districtwide to give students time to be with their families, and counselors would be available starting Friday, said Jefferson School District Superintendent Chad Martin.  

Adela Rodriguez, left, walks with her son, Yandel Rodriguez, 12, at the high school where people were evacuated after the shooting. (AP)

Adela Rodriguez, left, walks with her son, Yandel Rodriguez, 12, at the high school where people were evacuated after the shooting. (AP)

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"This is the worst nightmare a school district could ever face. We prepare for it," Martin said, "but you're never truly prepared."  

Police tape surrounded the school, which has about 1,500 students in sixth through eighth grades, and small evidence markers were placed next to spots of blood on the ground.  

Lucy Long, a sixth-grader at Rigby Middle School, told the Post Register newspaper in Idaho Falls that her classroom went into lockdown after they heard gunshots, with lights and computers turned off and students lined up against the wall.  

Lucy comforted her friends and began recording on her phone so police would know what happened if the shooter came in. The audio contained mostly whispers, with one sentence audible: "It’s real," one student said.  

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Lucy said she saw blood on the hallway floor when police escorted them out of the classroom.  

Jefferson County Prosecutor Mark Taylor said decisions about criminal charges wouldn't be made until the investigation is complete but that they might include three counts of attempted murder.  

Fox News' Stephen Sorace, Louis Casiano and the Associated Press contributed to this report.