Benazir Bhutto's widowed husband accused members of Pakistan's ruling regime of involvement in his wife's killing and called for a UN investigation, as British officers aiding Pakistan's own probe pored over the crime scene. "An investigation conducted by the government of Pakistan will have no credibility, in my country or anywhere else," Asif Ali Zardari, the effective leader of Bhutto's opposition party, said in a commentary published Saturday in The Washington Post. "One does not put the fox in charge of the hen house." Calls for an independent, international investigation have intensified since the former prime minister was killed December 27 in a shooting and bombing attack after a campaign rally. Opposition activists denounced the government's initial assessment that an Islamic militant was behind the attack and that Bhutto died, not from gunshot wounds, but from the force of the blast. President Pervez Musharraf acknowledged that investigators may have drawn conclusions too quickly and mishandled evidence, including hosing down the site hours after the attack. But he insisted the government was competent to run the investigation with the help of forensic experts from Britain's Scotland Yard. The United States said it did not believe a UN investigation was needed.