Why did Nathan Bedford Forrest testify before Congress in 1871?

Nathan Bedford Forrest was ordered to appear before a congressional hearing in 1871 because of his role as the first grand wizard of the Ku Klux Klan. Although he had ordered the organization to be disbanded in 1869, local chapters continued to engage in campaigns of intimidation and violence against Black Southerners and Republicans, prompting the federal investigation into the group's activities. During his testimony, Forrest denied his membership in the organization.1