In writings reportedly recovered from Harper-Mercer's computer, the gunman is portrayed as feeling hopeless, identifying with other mass shooters, and determined in his actions.
People.com, which cites a source close to the investigation, reported Monday:
Mercer then purportedly expresses skepticism that anything could have turned his life around: "He asks, 'What was supposed to happen? What great event was supposed to make me realize I had so much going for me?' " the source says.
Abandoned and alone, Harper-Mercer allegedly writes, "I've been forced to align myself with these demons and become one of them. At first, it was involuntary, but now I am aligned with them. I now serve. When I die I will become one of them."
He adds: "My success in Hell is assured."
People.com notes in its report that the unnamed source only read parts of Harper-Mercer's alleged manifesto to the publication and it did "not received a copy of this document nor confirmed its existence."
Harper-Mercer's manifesto also refuted claims by others who thought he was "crazy," and asserted that in fact he was "the sane one," according to another unidentified official with access to the document, The Associated Press reported.
Harper-Mercer, who was discharged in 2008 from the U.S. Army for "failing to meet the minimum administrative standards" while still in basic training, suffered from poor mental health, according to his mother.
Law enforcement officials recovered 14 legally purchased guns from the home Harper-Mercer shared with his mother, who is also reportedly a gun enthusiast. He had six guns in his possession when he carried out the attack at Umpqua Community College, The New York Times reports in an article about the gunman's mother's writings on the Internet.
Local Roseburg Pastor Randy Scroggins, addressing his New Beginnings Church of God congregation on Sunday, shared his thoughts on whether he could forgive the 26-year-old gunman.
"Can I be honest? I don't know. That's the worst part of my job. I don't know. I don't focus on the man. I focus on the evil that was in the man," Scroggins said.