A new police officer on Thursday took over the probe into the deadly suicide attack on former Pakistan Premier Benazir Bhutto's motorcade in Karachi after she alleged that the previous officer was involved in torturing her husband in 1999.Deputy Inspector General Saud Mirza took over as the head of the special police team investigating the bomb blasts that killed nearly 140 people and injured hundreds others.The Interior Ministry had said on Wednesday that DIG (Investigation) Manzoor Mughal, who was earlier heading the probe, would be replaced due to objections raised by Bhutto's Pakistan People's Party.Bhutto had alleged that Mughal was present when her husband Asif Ali Zardari was tortured while in police custody in 1999 and was saved only due to the intervention of the judiciary and top diplomats.While the Interior Ministry maintained that Mughal had gone on leave, officials in Karachi said the provincial government had no doubts about his professionalism but it had decided to replace him so that there would be no accusations of impartiality regarding the investigation.Sindh Chief Minister Arbab Ghulam Rahim has said the entire police team probing the blasts would be replaced in the interest of impartiality.The government has, however, firmly rejected Bhutto's demand for roping in foreign experts for the probe, saying Pakistani investigators have the necessary expertise to handle the matter."We know what we're doing. We don't need assistance," Prime Minister Shaukat Aziz said.Investigators have now come to the conclusion that the attack was carried out by two suicide bombers. The blast triggered by the second bomber was more devastating and caused most of the deaths.The head of the second bomber, which was badly mutilated, has been reconstructed by doctors and military experts. The investigators believe both bombers were Pakistanis.They have also said there were similarities between the blasts in Karachi and other recent suicide attacks, including one on the mess of an elite army commando unit at Charsadda near Islamabad.