Benazir Bhutto looks on to supporters during campaign rally in Rawalpindhi, 27 Dec 2007

The controversy over exactly what caused Pakistan's former Prime Minister Benazir Bhutto to die last week is growing with the release of an inconclusive medical report and new video footage that casts doubt on the government's explanation.

Pakistan's Interior Ministry says Ms. Bhutto was killed when the force of a suicide bombing slammed her head into a lever for the sunroof in her armored vehicle.

But several of Ms. Bhutto's close aides, including one who was with her when she was rushed to the hospital, and her husband, Asif Ali Zardari, say they are sure she died from a bullet wound to the head.

Monday, news organizations published the contents of a medical report by doctors at the hospital where she died which said that no determination was made about whether she was shot.

It gave the cause of death as open head injury with depressed skull fracture, leading to cardiopulmonary arrest. The report said without an autopsy, no doctor would ever be able to give a conclusive opinion on the matter.

Doctors say their request for an autopsy was denied by a police chief.

Ms. Bhutto's widower says he refused to allow the government to conduct an autopsy because he did not trust the authorities to carry out a credible investigation. Ms. Bhutto was buried on Friday.

Meanwhile, new video footage of the attack, obtained by Britain's Channel 4 television, shows a man firing a pistol at Ms. Bhutto as she poked her head out of her vehicle's sunroof to greet supporters.

The video shows her hair and shawl jerking upward. She then falls into the vehicle just before an explosion -- detonated by a suicide bomber -- rocked the car.

Members of Ms. Bhutto's Pakistan People's Party are demanding an international probe into her death.

Some information for this report was provided by AFP, AP and Reuters.