On June 20, 2002 the supreme court ruled that it was to be made illegal for the death penalty to be handed out to inmates who have mental issues. This rule was put into force because it was felt that it was in violation of the 8th amendment.
Also in 2005 it was ruled that juveniles under the age of 18 at the time of their crimes would nit be handed the death penalty. The trend since 2002 shows that the supreme court has slowly been outlawing the death penalty.