President Biden strongly condemned racist conspiracy theories in a speech Tuesday after visiting Tops Friendly Markets grocery store, the site of a mass shooting in Buffalo, N.Y., where 10 people were killed in an alleged hate crime over the weekend.

Mr. Biden choked back tears as he named the victims of the shooting. “In America, evil will not win, I promise you; hate will not prevail, and white supremacy will not have the last word,” he said.

The shooting suspect, 18-year-old Payton Gendron, appears to have been motivated by racist conspiracy theories he discovered on Internet message boards during the pandemic, according to a document posted online that police believe he wrote.

In the 180-page document, the writer describes himself as a fascist, a white supremacist, a racist and anti-Semitic. It includes details of a planned incident similar to what occurred on Saturday, including the writer’s goal to kill as many Black people as possible. It describes a conspiracy theory known as the ”great replacement” that asserts political elites use immigration and other policies to reduce the white population.