Washington police have apprehended a high school student whose mother found journal entries outlining plans to attack his school and alerted authorities.

The 17-year-old’s journal had information about an attack he was preparing at College Place High School on April 20, 2020, the 21st anniversary of the 1999 Columbine High School shooting, CNN reports.

Officers took the student into custody with no incident on Tuesday after he came home from school. He was subsequently booked at a juvenile center for felony harassment and threats to bomb or injure property. Police said they found more writings in the teen’s bedroom that supported this purported plot. “We did not locate any firearms or explosives in the teen’s possession. However, we did locate literature on how to develop explosives and other weapons,” College Place officer Dylan Schmick told HuffPost.

The spree at Columbine in Littleton, Colorado left 12 students and one teacher dead. It still ranks as one of the worst mass shootings in U.S. history, and one of the deadliest episodes of school violence.

“The mother was very emotional and loves her son,” police chief Troy Tomaras said in a statement. “This was not an easy thing to do, but it was the right thing to do. The mother wanted to prevent others from being hurt and wants her son to get the help he needs.”

The school’s resource officer was also included in the investigation and warned school officials of the incident.