Kansas City, Mo. ? Two Platte City teenagers charged with threatening to conduct an armed attack on their high school to mark the seventh anniversary of the Columbine High School killings made their first appearance in court Tuesday.

An associate circuit court judge entered not guilty pleas for Trevor P. Fattig and Sean M. Amos, both 17. Each is charged with a felony count of making a terroristic threat and are being held on $15,000 bond. If convicted, they face up to four years in prison.

Prosecutors said the two told classmates at Platte County R-3 High School that they were planning a “Columbine-type” incident at the school on Thursday, the seven-year anniversary of the attack in suburban Denver in which two students killed 12 classmates and a teacher, wounded 24 others, then committed suicide.

According to court documents, the two said they planned to bring an AK-47 assault rifle and a “Magnum” handgun to school and plant explosives in the gymnasium. They would then force an assistant principal at gunpoint to call for a school-wide assembly where they would then open fire, killing the assistant principal, students and faculty.

The five students Fattig and Amos talked to told school administrators, who brought in law enforcement, officials said.

Platte City Police Sgt. Elizabeth Willoughby said police searched Amos’ house and found no evidence of weapons or explosives. She said authorities would likely seek a warrant to search Fattig’s house soon.

In a probable cause statement filed in the case, Willoughby said Fattig told her he “has ‘violent thoughts’ all day.”

Eric Zahnd, the county’s prosecuting attorney, said the presence of weapons was not required for a conviction.

“The threat itself is a crime,” Zahnd said, adding that the state created the charge of making a terrorist threat in 1999, partly in response to the Columbine killings.

“It appeared that (Fattig and Amos) had a very detailed plan,” Zahnd said. “I wasn’t willing to sit idly by and see what happened on April 20.”