Teen charged for threatening to 'shoot 400 people for fun,' police say She told coworkers that she purchased a AK-47 and had the urge to shoot people.

Police arrested an Oklahoma teenager with a semi-automatic rifle this week after she allegedly threatened to target her former high school and "shoot 400 people for fun."

Alexis Wilson, 18, was arrested at her home on Monday after allegedly telling coworkers at a pizza restaurant in McAlester, Oklahoma, about 90 miles south of Tulsa, that she purchased a new AK-47 and had the urge to shoot people, according to police.

The coworkers reported Wilson's comments after she left, claiming she had showed them videos and images of her firing the rifle and noted that "there were so many people" at McAlester High School, where she previously attended, that she would like to shoot, according to an incident report.

Officers with the Pittsburg County Sheriff’s Office said they found the rifle in Wilson's bedroom, as well as a 12-gauge shotgun, six high-capacity magazines and rounds of ammunition. She was charged with a felony for making a terrorist threat against the school.

"This is probably everybody's biggest fear in the United States right now -- a school shooting," Pittsburg County Sheriff Chris Morris told ABC News in an interview Tuesday. "Lots of people don't want to acknowledge that this, an active shooter or school violence, is probably the biggest threat in America right now."

He said he was proud of his deputies for acting fast on the claims because all threats of this nature must be taken seriously in today's climate.

"There's no time to sit around and wait on it. I don't want one of my schools in my county shot up. I don't want anybody hurt," he said. "So when I got the information, I spoke with my deputies and I told them not to go home until they had it resolved and taken care of."

Officials at McAlester High School said Wilson dropped out during her freshman year and had previously been suspended for bringing a knife to school and having a swastika symbol on her belongings, investigators said.

Wilson told police that she had recently completed a program at a camp for troubled youth and tried to enroll back into McAlester High School, but they didn't allow her to, according to the incident report.

Investigators said she seemed "very upset" about not being allowed to return to school, but she denied being mad about it. She said she was previously angry about being bullied by other students, but not anymore.

"Alexis also then stated to me that she used to be suicidal and border line homicidal to the people of Mcalester School because she was bullied," one of the arresting officers wrote in the incident report. "I asked Alexis if she had thought about hurting anyone at the school and she stated not recently but she has in the past."

Wilson was being held on $250,000 bond at the Pittsburg County Jail as of late Tuesday. She pleaded not guilty at her arraignment on Monday and is scheduled to appear in court again on Sept. 27.