ROCKVILLE, Md. (AP) — An 18-year-old Maryland high school student was charged with planning to commit a school shooting after investigators reviewed the teen’s writings and other material, including internet searches and messages, police said Thursday.

The student was arrested Wednesday by the Montgomery County Police Department.

The investigation began after a person contacted police in the Baltimore area, saying he met the teen in a psychiatric facility. The person alerted authorities to the teen’s writings, which were labeled a fictional account by their author, according to court records. But investigators wrote that they believed the document was based on the teen’s life, not entirely fictional.

The writings, which the teen called a memoir, spanned 129 pages and included an account of a character who plans a school shooting but ultimately is taken into law enforcement custody and then receives psychiatric treatment, according to police.