sting to it the primary responsib- ility for developing relevant facts on which a determination of guilt or Xmocence can be made. See United States I. Nixon, 418 U.S. 683, 709, 94 S.Ct. 3090, 3108, 41 Page 11 L.Ed.2d 1039 O974); Williams /. Florida, 399 U.S. 78, 82, 90 S.Ct. 189)1896, 26 L.Ed.2d 446