OXFORD TOWNSHIP, Mich. (NewsNation Now) — Two Michigan sisters said there were threats about a shooting posted on social media for weeks before a teen opened fire at a high school Tuesday, killing three other students and wounding eight other people.

“It kind of seemed inevitable that it was going to happen,” Haley Hull said on “NewsNation Prime.”

Haley works near Oxford High School in Oxford Township, a community about 30 miles north of Detroit.

She called her sister Krista, a student, after seeing police cars head toward the school.

“All I heard was just her whispering and I heard, like, silent sobs going on in the background,” Haley said. “And then over the PA, I just heard that there was an active shooter in the building.”

Authorities say a 15-year-old sophomore opened fire.

“I didn’t know if my sister would make it out alive,” Haley said.

Krista was in a classroom when she heard the shots.

“It sounded like something was banging,” Krista said. “And, like, we weren’t sure what it was. And then we, like, heard gunshots and my teacher, like, ran really fast to … lock the door.”

Krista said active shooter training had prepared her for such a situation. Within the last two weeks, she had asked her mother if she could leave school, fearing a possible shooting.

“My sister was blowing up my mother’s phone asking her to pick her up from school, saying that there is a school shooting threat,” Haley said. “She doesn’t want to be here. She feels unsafe.”

Undersheriff Mike McCabe said that authorities were aware of allegations circulating on social media that there had been threats of a shooting at the roughly 1,700-student school before Tuesday’s attack, but he cautioned against believing that narrative until investigators can look into it.

Investigators are still trying to determine a motive for the shooting.