The Scotland Yard team charged with establishing the cause of the death of Benazir Bhutto conclude that she was propelled by a bomb blast into the lip of the escape hatch of the armoured vehicle in which she was leaving a rally in Rawalpindi on December 27 last year.

They believe that the attack was a single-man operation, that the gunman identified in media footage of the bombing was also the suicide bomber who was close behind the vehicle and whose blast killed the leader of Pakistan’s opposition party.

Their attempts to establish these conclusions were hampered by a lack of available evidence. They complain of a lack of “an extended and detailed search of the crime scene, the absence of an autopsy and the absence of recognised body recovery and victim identification processes”.

Instead the team relied heavily on X-rays of Mrs Bhutto’s head, taken at the Rawalpindi General Hospital following her death – verified as genuine via a comparison with her dental records. They also spoke to medical staff who were involved in her treatment and to family members who washed her body before burial.

Her only apparent injury was a major trauma to the right side of her head. The UK experts agreed that this was not an entry or exit gunshot wound. Accounts from medical staff and family helped them discount the idea that she could have been shot in her torso or lower body - she was in any case largely inside an armoured vehicle.

With only limited X-ray material, without a full post-mortem examination and without the more detailed images that could have been provided by a CT-scan, investigators could not categorically rule out the possibility that she was shot in the neck or upper body, though the evidence suggests there was not.

The possibility of any such gunshot wound became irrelevant to the business of establishing the cause of death when the investigators examined the severity of her head injury. “The only tenable cause” of this injury, according to the Home Office pathologist consulted, was an impact caused by a bomb blast.

The injury was too severe to have been sustained while simply ducking down into the vehicle. They say the type of high explosives used in the attack, so close to Mrs Bhutto, would generate “significantly more force than would be necessary” to cause such a head injury.

The escape hatch was not, as has been reported, a sunroof. It was designed to be used solely as a means of escape from the armoured vehicle, which itself was designed to withstand gunfire and bomb-blasts. The hatch has a solid lip with a depth of 9mm. The investigators say her head injury is “entirely consistent” with a collision with this lip.

This conclusion was backed up using video footage in which her head does not completely disappear from view until 0.6 seconds before the blast. Then she moves forward and to the right as she ducks down into the vehicle.

“The overwhelming conclusion must be that she did not succeed in getting her head entirely below the lip of the escape hatch when the explosion occurred,” the report states.

Contrary to speculation that two attackers were involved, a gunmen and a suicide bomber, the investigators conclude that the gunman was also the bomber, and offer three reasons for this conclusion.

Media footage shows the gunman behind the vehicle and does not show any other attacker.

A forensic explosive expert placed the bomb blast as originating from the same place, between 1-2 metres from the back of the vehicle with no-one in between. If there was another attacker in the same place, it is highly unlikely that he would have survived.

Body parts from only one individual remain unidentified: experts believe these come from the suicide bomber.

The investigators concluded that the gunman fired the shots before detonating the bomb.

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