Mughal said the head of the suspected bomber had been found, and it was estimated he had 15 to 20 kg of explosives strapped to his body. Typically, the upward force from a blast blows off the head an attacker.
Bhutto said there were also shots fired at her vehicle during the attack, while a man armed with a pistol and another wearing a suicide belt were arrested earlier.
DISTRUST
There was no claim of responsibility.
Baitullah Mehsud, a well-known Pakistani Taliban commander said to have issued assassination threats against Bhutto, telephoned Reuters to deny any involvement in the attack.
The government said police were investigating whether the attack had links to tribal regions bordering Afghanistan which have become hotbeds of support for al Qaeda and the Taliban.
"Definitely, it is the work of the militants and terrorists," Interior Ministry spokesman Javed Iqbal Cheema said.
The scale of Thursday's reception for Bhutto proved she has the mass appeal no other leader can muster despite being out of power for 10 years, and out of Pakistan for eight.
Bhutto's re-entry to the political scene was welcomed by investors who saw her as a force for democracy and stability, who would help Pakistan keep consistent economic policies.
The Karachi share index <.KSE> dipped about one percent in early trade in reaction to the attack, but recovered to barely changed at 14,787.55 points, just short of life highs and showing a gain of almost 47 percent since the start of the year.
The United States, the European Union, and other allies condemned the attack along with neighbours India and Iran.
Most shops in Karachi stayed shut on Friday, schools were closed, there were no buses and few taxis, and many people stayed at home following the carnage overnight.
Families and friends of the blast victims started to bury their dead, including six police, later on Friday.
"Father don't go away, don't take my father away," Zeeshan the 9-year-old son of Inspector Shahab-ud-din cried as his father's coffin was lowered into the ground.
Suicide and roadside bomb attacks have multiplied since troops stormed Islamabad's Red Mosque to crush an armed student movement in July. Two bomb blasts struck the northwestern cities of Peshawar and Dera Ismail Khan on Friday, wounding two people.
