Gregg v. Georgia
Other Justices said Georgia's use of the death penalty was discriminatory.  They wrote that black defendants seemed more likely to get the death penalty than whites.  This would violate the Fourteenth Amendment, which says that the states must give every person "the equal protection of the laws."  If a certain group, like black people, is more likely to get the death penalty just because of their race, they are not being treated equally under the laws.