A Wisconsin teen who is accused of fatally shooting his grandparents had reportedly planned to carry out an attack on his high school.

Alexander M. Kraus, 17, was arrested at the home of Dennis and Letha Kraus, 74 and 73, at their Grand Chute home. The Green Bay Press-Gazette reported that the teen was at the residence as police performed a welfare check and took him into custody.

“He was still at the scene. He came back to the police department, spoke with investigators, he was cooperative,” Grand Chute police officer Travis Waas said, according to WBAY.

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The Associated Press reported that Alexander confessed to killing his grandparents. Waas told local media that Alexander carried out the slayings with a long gun.

Alexander, a junior at Neenah High School, reportedly also revealed that he planned to carry out an attack at the school on Monday. According to a statement released by the school district, Grand Chute police informed them of the teen’s arrest and his plans to “cause harm” at the high school.

While authorities reportedly recovered documents related to his plan, they haven’t disclosed any details regarding the thwarted attack.

“Police have indicated that there is no danger to students and staff at the high school and the school day on Monday will proceed as normal,” the Neenah Joint School District said, according to KLUK.

“We are appreciative of the work of our local law enforcement and this is another reminder for all of us to remain vigilant in keeping each other safe.”

The 17-year-old is charged with first-degree intentional homicide. He remains jailed as he awaits his initial court appearance on Tuesday.

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[Featured image: Alexander Kraus/Outagamie County Jail]