Zardari, Bhutto's husband, said a Pakistani investigation into the 2007 assassination of the former prime minister would be made public and the culprits would be brought to justice, Pakistani newspaper The Nation reports.
He said he would continue his leadership in the spirit of Bhutto, adding revenge would come through Pakistani democracy.
"Investigations will soon be completed and made public," he added.
A U.N. report on the assassination implicates the government of former Pakistani President Pervez Musharraf, claiming Pakistani officials at the time "failed profoundly" to protect her.
The U.N. report on the Dec. 27, 2007, death of Bhutto in Pakistan's garrison city of Rawalpindi also dismissed a subsequent investigation into her death as prejudiced.
"The commission believes that the failures of the police and other officials to react effectively to Ms. Bhutto's assassination were, in most cases, deliberate," the report said.
Musharraf aides called the report a ''pack of lies.''
Bhutto was killed following a campaign rally for her Pakistan People's Party. She had returned to Pakistan from exile to run in January 2008 parliamentary elections.
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