The bomber's badly burnt head was recovered from the scene of the blast in a park in Rawalpindi, where Bhutto had been holding a political rally.

Saud Aziz, the city's police chief, said investigators would reconstruct the head and take DNA samples from other body parts found nearby in the hope that they could quickly identify the killer. “It is too early to say who may have been responsible,” said Aziz.

Witnesses said Bhutto was shot as she stood up through the sunroof of her four-wheel drive vehicle.
Photographs taken moments before she died show her wearing her white headscarf and looking out over tightly packed, cheering crowd of supporters. The images then show the scene being swallowed in a large, orange fireball as the attacker's bomb detonated.

Other tests will allow investigators to determine the type of explosive used. This is only the beginning of the inquiry. Pakistani officials today said they already had evidence linking both al-Qaida and the Taliban to the assassination.

However, there is already deep mistrust in Pakistan among many, not just Bhutto's supporters, who doubt that a small cell of extremists alone was responsible for her death.

At the heart of these fears lies the long and dangerous association of the Pakistani government and its military with Islamic militants, both in Afghanistan and in Kashmir.

Even Bhutto herself warned before her death that there were powerful figures in Pakistan plotting to kill her.
Two days before her return, Bhutto sent Musharraf a letter, giving names and telephone numbers of several men she believed were plotting against her.

Reports in the Pakistani press said the men included an official in the Pakistani intelligence agencies, a member of the National Accountability Bureau, which has long investigated corruption cases against her, and a former provincial government official.

Then, after the first attack on the day of her return, Bhutto asked for international investigators to be assigned to the case. Her request was rejected. Al-Qaida, or militants allied to the group, might have had a lot to lose if Bhutto had won, as expected, next month's elections. She had spoken repeatedly of her plans to take on the rising tide of militancy sweeping Pakistan.

Ayman al-Zawahri, al-Qaida's number two, spoke out against Bhutto's return in a video recording this month and called for attacks on all candidates in next month's election.

Bruce Riedel, a senior fellow at the Brookings Institution and former senior director for South Asia on the National Security Council, said al-Qaida had been trying to kill Bhutto for many years.

"If it's not them, it's certainly one of the groups that are sympathetic with them," he said. "They all work together and share a common antipathy to Bhutto because she's a woman, an advocate of secularism, a supporter of democracy and everything they stand against."