In this representational photo, a driver who failed a field sobriety test at a DUI traffic checkpoint stands in handcuffs waiting to be processed in Miami, Florida, June 4, 2007. Joe Raedle/Getty Images

A Wisconsin teen confessed to killing his grandparents and plotting to carry out an attack on his high school, police said Monday.

Alexander M. Kraus, 17, was arrested Sunday on two counts of first-degree intentional homicide – each carrying a life sentence if convicted – hours after the police, responding to a 911 call, discovered the bodies of 74-year-old Dennis Kraus and 73-year-old Letha Kraus in a Grand Chute home at around 11:30 a.m. local time (12:30 p.m. EDT). "He [Alexander] was still at the scene. He came back to the police department, spoke with investigators, he was cooperative," Grand Chute Police Officer Travis Waas told ABC-affiliated WBAY.

The police learned during interrogation that the teenager also planned to cause harm Monday at Neenah High School, where he is a junior. "That information was learned by our investigators, in speaking with the suspect. Immediately we reached out to the Neenah Police Department and the Neenah Area School District and turned that information over to them," Waas said.

The exact nature Alexander’s plans were not released by the police or the school district officials. Authorities said they were confident the teenager was acting alone. There was heavy police presence at the high school Monday.

"I understand there's a ton of questions coming from the community, relationship from the family, who had called 911. All of that information will be released in the criminal complaint that will answer all of these questions," Waas said. "We're not trying to withhold information. We're not trying to create barriers, we're just trying to release information that we can, at a certain period of time, just out of respect for the victim's families."

The school district released the following statement regarding the incident: "Grand Chute police informed the Neenah Joint School District that the student arrested on two counts of first degree intentional homicide on Sunday also had a plan to cause harm at Neenah High School. 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. Additional counselors are available to students and there is an extra police presence as an additional precaution. 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.”

Alexander was scheduled to make his first appearance in the court Tuesday. Meanwhile, police were continuing with their investigation, including the execution of search warrants for laptop, cell phone and other electronic devices belonging to the suspect. “This is still an active and ongoing investigation with several search warrants already being executed with more expected. Again, we believe this to be an isolated incident, with no danger to the public,” the police said in a press release.