Complex sentence: Before the Columbine High School massacre, one of the Columbine High School student mass murderers Dylan Klebold referenced lyrics from Nine Inch Nails multiple times in his journal, and heavily identified with the protagonist of the album as a symbol of his own depression.
Split into simpler sentences: Before the Columbine High School massacre, one of the Columbine High School student mass murderers Dylan Klebold referenced lyrics from Nine Inch Nails multiple times in his journal. Klebold heavily identified with the protagonist of the album as a symbol of his own depression.