Benazir was slain just hours before she was to go public with "proof" that Pakistani intelligence and electoral officials were planning to rig polls, an official from her party said on Tuesday.
Opposition leader Benazir was to unveil a report about an alleged plot to rig the country's general elections at a press conference on Thursday night after giving it to visiting US lawmakers, said Senator Latif Khosa.
"Benazir was scheduled to reveal a document containing proof of rigging plans by the election commission and Inter-Services Intelligence (ISI) the night she was assassinated," Khosa told AFP.
"It was a 160-page document 'Yet another stain on the face of democracy', which Benazir was to unveil at a press conference in Islamabad on December 27 after meeting the two visiting US lawmakers," he said.
"But that was not possible because she was murdered." Khosa did not give the names of the US lawmakers said to have been visiting. Pakistan government officials were not immediately available for comment.
Khosa said the document presented evidence that the military-run ISI, Pakistan's main spy agency, colluded with the election commission and the former ruling party to fix the result of the polls.
"The financial assistance provided by the US for preparation of computerised electoral rolls was misused," he said. He also alleged that the government gave a contract for the printing of the electoral lists to a close relative of the chief of the Pakistan Muslim League-Q party, which was in power until November.
"We collected substantial evidence of rigging being planned for the January 8 election from different sources and incorporated it in the report," Khosa said. He did not say what the party now planned to do with the document. A spokesman for the election commission said earlier on Tuesday that holding the polls on schedule now "looks impossible", adding that the body would announce the date for the vote on Wednesday.