Dylan Roof (right), the suspect in the mass shooting that left nine dead in a Charleston, S.C., church in June 2015, appears in court accompanied by assistant defense attorney William Maguire July 18, 2015, in Charleston, S.C.
Grace Beahm-Pool/Getty Images)

Accused Charleston, S.C., shooter Dylann Roof "self-radicalized" online, adopting viewpoints that were reportedly acquired through material found online and elsewhere, federal prosecutors say, the Washington Post reports.

According to the report, rather than adopting his beliefs “through his personal associations or experiences with white supremacist groups or individuals or others,” prosecutors say, Roof adopted his white supremacist beliefs from the internet.

The 22-year-old, who is accused of killing nine black parishioners—including pastor and state Sen. Clementa Pinckney—at Charleston's historic Emanuel African Methodist Episcopal Church, could face the death penalty in both the federal and state cases against him for the horrific mass shooting.

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Roof was indicted on federal hate crime charges that he attacked the parishioners“because of their race and in order to interfere with their exercise of their religion," Attorney General Loretta Lynch said.

In the state case, he will face nine counts of murder and three counts of attempted murder in the June 2015 shooting.

According to the Post, in a court document filed Monday, authorities announced their intention to call on experts to outline how Roof's comments, writing and media consumption “are consistent with the adoption of a white supremacy extremist ideology, including a belief in the need to use violence to achieve white supremacy.”

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Prosecutors say Roof's "self-learning process" led him to believe “that violent action is necessary to fight for white people and achieve white supremacy … and that the choice of targets and execution of violent action should be conducted in a manner that promotes these objectives, to include publicizing the reasons for those actions to inspire others to engage in violent action to further white supremacy.”

Additionally, federal authorities said they uncovered two new handwritten manifestos and a list of churches. One manifesto was found in Roof's jail cell, while the other was uncovered in his car.

After the attack on the church, often referred to as Mother Emanuel, officials found an online manifesto linked to Roof that showed a deep-seated hatred toward blacks.

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Read more at the Washington Post.