event was prevented. >> reporter: a possible school shooting for did. authorities arrested 18-year-old alex ye, charging the high school student previously hospitalized for psychiatric treatment with making threats of mass violence at his high school and elementary school in rockville, maryland. according to charging documents, a friend alerted local police of a chilling 129-page memoir, a story of a bully transgender teens desire to shoot up a school. elements police say are pulled from the suspects real life. >> even after being removed from the school, ye said he would do something at graduation because he lived close to school. ye was preoccupied with self harm, school shootings, and explosives. >> eporter: police say he google search to other mass shootings, including sandy hook and nearby gun ra ranges. police also recovered a bb gun from the suspect's home.