Mexico's deputy attorney general today made sweeping accusations that his own boss and two of the country's most powerful officials conspired in the Sept. 28 assassination of his brother -- the ruling PRI party's reform-minded secretary-general. He then resigned from his post and the PRI. At an angry, 45-minute news conference this morning, Mario Ruiz Massieu said he's given the government evidence that the PRI's president and secretary-general (the second- and third-most powerful Mexican officials ) had blocked his investigation into the shooting of Jose Francisco Ruiz Massieu , Mexico's No. 2 official and a future presidential contender. He also said his boss, Attorney General Humberto Benitez Trevino, joined in the cover-up. Ruiz Massieu distributed a 97-page book he said contained "proof" of the alleged misdeeds.