After several hours standing on the truck, Bhutto’s ankles were swelling and she decided to sit down for a few minutes. She made her way down some steps to a secure cubicle located behind the driver’s seat. It was then the attack began: two bombs went off in rapid succession. The first killed, among others, three policemen and opened up a path through which the second bomber was able to move.

The attack left 149 people dead and 402 wounded. But it missed its mark. As rescuers worked by the light of the flames, dragging bodies from the twisted wreckage, Bhutto stepped out of the vehicle without a scratch.As soon as the smoke had cleared people were asking whether the first bomb had been remote-controlled. The issue was significant because the police had supposedly provided the convoy with two jammers to block any radio signals intended to detonate a bomb. Activists from Bhutto’s party claimed the jammers either hadn’t been provided or had been switched off. Both the Karachi and Rawalpindi attacks were investigated by Joint Investigation Teams (JITs) that brought together various police departments. The JIT report into the Karachi attack concedes that the Turkish-made jammers were not functioning at the time of the attack. According to a Sindh Special Branch memo, they failed because their batteries had been drained over the long course of the procession. It was a moot point. Perhaps anticipating that jammers would be deployed, the bombers had anyway decided against remote detonation: it was a double suicide attack.

Pakistan lacks skilled forensic pathologists but there have been so many suicide attacks now that even the most junior policeman knows that the first thing to look for is the ‘facemask’. For some reason, related to the way the shockwave moves from the bomb-laden waistcoat, the bombers’ faces - though very little of the head behind them - often survive intact. On this occasion, the JIT report states, one facemask was found 26.6 feet away from the point of detonation and another 78 feet away. To whom did they belong?

The Pakistani police rarely know whether their political masters want an investigation to be thorough or not. As a general rule they assume the politicians are hoping for a cover-up and actively investigate only when specifically ordered to do so. That would explain why the JIT Karachi report is such a remarkably poor piece of work: 138 pages long, it contains virtually no useful facts and plenty of contradictions. Page after page of police reporting from the scene establishes only that some vehicles were destroyed and that a lot of body parts were strewn about. Some of these were gathered and sent to the morgue while others (no explanation is given as to why) went to a DNA specialist, who concluded that the parts he had were from different people. The finding had no discernible significance. Basic, easily discoverable facts were not gathered.

The various police documents give the time gap between the first and second explosions as between 30 and 50 seconds (Inspector General of the CID); under a minute (the Federal Investigation Agency); one minute exactly (an army explosives expert); and between one and two minutes (the bomb disposal unit travelling with the convoy). Some of the documents in the JIT report - presumably those from the intelligence agencies - are unattributed. Others, such as doctors’ handwritten notes on the death of a few, apparently randomly selected victims, are irrelevant. Indeed, the whole report has only two findings of any significance.

The first concerns the devices called ‘strikers’ that most suicide bombers in Pakistan rely on to detonate their explosives. Although its lot number was illegible, the striker sleeve found at the epicentre of the Karachi blast was marked MUV-2. The suicide attack in Karachi was the 28th to occur in Pakistan in 2007. MUV-2 striker sleeves had been used on 11 of those occasions, including bombings in Quetta, Rawalpindi, Peshawar and other smaller cities in North-West Pakistan. The targets in these 11 cases were all consistent with the Taliban having been responsible and included the police, politicians who had opposed jihadis and the Frontier Corps, which had done much of the fighting against the Taliban.

The second interesting entry was a summary of the interrogation of the man Bhutto had named, Qari Saifullah Akhtar. But the document had been doctored. After describing his childhood and his long jihadi career, the story came to an abrupt end in August 2007. It resumed in January 2008, after Bhutto’s murder had been carried out. It was a clumsy effort: the edited page is in one font, the rest of the document in another.

The JIT may have provided few answers, but it did inadvertently hint at the reason some in the deep state were so anxious about Bhutto. The report includes newspaper articles providing possible motivations for an attack on Bhutto. One quotes her as saying that if the US identified the whereabouts of Osama bin Laden on Pakistan soil she would consider co-operating with Washington in having him detained.

That in itself might have provided enough motive for an attack. But there was something else. As part of her effort to win American support, Bhutto said that she would be willing to hand over the Pakistani nuclear scientist AQ Khan for questioning by the IAEA. At the time, Khan had accepted personal responsibility for the export of nuclear technology to Iran, North Korea and Libya, although his live TV confession of his activities was always considered suspect by the IAEA and the US, both of which believed that no single individual could have exported planeloads of nuclear material without the army’s knowledge. To this date, the military, despite insistent requests, has refused to allow foreigners to talk to Khan. Bhutto’s offer to the IAEA was seen as a real threat to Pakistan’s nuclear status.

Despite their apparent lack of interest in the failed assassination attempt, the Karachi police did eventually arrest someone. In June 2010, they raided the home of Azmatullah Mehsud, seized a pistol and accused him and his brother Abdul Wahab Mehsud (who remained at large) of involvement in the attack. As so often, the motivation of the police was unclear. It seemed Azmatullah had been arrested not so much as a result of the Bhutto case but because the police thought he was going to attack one of their own officers. The senior superintendent of the Karachi CID, Umar Shahid, told a local paper: ‘We have recorded his telephonic conversation with his brother, who directed him to attack me.’

The police have leaked a few snippets of information about Azmatullah to the press. They have said he raised funds for the Taliban and provided hideouts and medical treatment to injured militants. They also said he had links to Baitullah Mehsud, the leader of the Pakistani Taliban, and the very violent anti-Shia group Lashkar-e-Jhangvi. Azmatullah was released the next month. But if some elements of the state wanted him free, others did not. A day later, a Sindh police anti-extremism cell re-arrested him. ‘Due to a shortage of evidence, the courts released several suspects on bail but he has been detained for further investigation,’ a police official said. His current whereabouts are not known.