Complex sentence: The U.S. Department of Justice concluded that Arizona sheriff Joe Arpaio oversaw the worst pattern of racial profiling in U.S. history; they subsequently filed suit against him for unlawful discriminatory police conduct.
Split into simpler sentences: The U.S. Department of Justice concluded that Arizona sheriff Joe Arpaio oversaw the worst pattern of racial profiling in U.S. history. The DoJ subsequently filed suit against him for unlawful discriminatory police conduct.