(AP)- President Pervez Musharraf said Thursday that uncertainty remained about the exact cause of Benazir Bhutto's death, despite an initial government report that she was killed when a bomb blast slammed her head into her vehicle.
"One should not give a statement that's 100 percent final. That's the flaw that we suffer from," Musharraf said at a news conference, noting that more evidence was emerging about the attack. "We needed more experience, maybe more forensic and technical experience that our people don't have. Therefore I thought Scotland Yard may be more helpful."
Musharraf said he also reached out to British investigators for assistance to dispel accusations that Pakistan's military or intelligence services were involved.
"We don't mind going to any extent, as nobody is involved from the government or agency side," he said.
Speaking a week after Bhutto's assassination in a shooting and suicide bombing, Musharraf denied there had been a security lapse and implied that Bhutto, who was greeting supporters through the sunroof of her armored vehicle at the time of the attack, was partly responsible.
"Who is to be blamed for her coming out (of) her vehicle?" he asked, adding that others in the vehicle had not been hurt in the attack.
Bhutto had been allowed to have the police superintendent of her choice in charge of her security, had four vehicles with a total of 30 officers with her, and 1,000 more police deployed at the Rawalpindi rally where she was slain, he said.
Musharraf said it was the responsibility of Bhutto's party leadership to stop supporters from swarming her vehicle, as any police action against them would have involved a baton charge or the firing of tear gas.
He conceded there were shortcomings in Pakistan's handling of the case, including the hosing down of the bomb site hours after the attack, widely seen as undermining a detailed forensic examination. But he dismissed any suggestion there was a plan to conceal evidence.
"I'm not fully satisfied. I will accept that: cleaning the area. Why did they do that? If you are meaning they did that by design I would not say no. It's just inefficiency, people thinking things have to be cleared, traffic has to go through," he said.
Musharraf also denied reports that al- Qaida was getting stronger in Pakistan, but said the country faced an increasing threat from Taliban militants.
He blamed Islamic militant leaders Baitullah Mehsud and Maulana Fazlullah for 19 suicide attacks in the past three months. Over the same period, militant-related violence killed 400 people and wounded 900 others, he said.
"We know that these two people are responsible," he said.
A day after Bhutto's killing, government officials accused Mehsud of orchestrating the attack. A Mehsud spokesman denied responsibility. Musharraf did not directly blame Mehsud on Thursday.
A senior police investigator said Pakistani police have already secured key evidence, including the suspected bomber's remains, two pistols and cell phones.
Scotland Yard investigators, with their superior forensic techniques, could help determine whether either pistol was fired in the attack and also could examine video, said the official, speaking on condition of anonymity because of the sensitivity of the investigation.
Bhutto's supporters have insisted that a U.N. probe would be the only way to reveal the truth behind her assassination. They have dismissed Musharraf's announcement that Scotland Yard will join the investigation.
"The mist of confusion will be cleared only if the regime accepts the party's demand for holding a U.N. inquiry into the assassination as was done in the case of Lebanese Premier Rafik Hariri's murder," said Farhatullah Babar , a spokesman for Bhutto's Pakistan Peoples Party.
"The regime has lost all credibility. Neither a domestic inquiry nor vague foreign involvement ... would lay to rest the lingering doubts and suspicions," he said.
The unrest following Bhutto's death prompted the government to delay parliamentary elections from Jan. 8 to Feb. 18, a decision criticized by both Bhutto's party and the other main opposition group, led by former Prime Minister Nawaz Sharif .
Although both parties said they would still run in the elections, opposition leaders called on Musharraf to resign.
"Free and fair polls are impossible under his leadership," said Javed Hashmi , a senior member of Sharif's party. "Such a thing is unthinkable if he is there."
A leading research group, the Brussels-based International Crisis Group, warned that Pakistan risks falling into civil war if Musharraf remains in power. The institute called on the United States - which continues to support Musharraf - to recognize him as "a serious liability, seen as complicit in the death of the popular politician" Bhutto.
"It is time to recognize that democracy, not an artificially propped-up, defrocked, widely despised general has the best chance to provide stability," the group's Asia director, Robert Templer , said in a statement accompanying the report.
"Unless Musharraf steps down, tensions will worsen and the international community could face the nightmare of a nuclear-armed, Muslim country descending into civil war," Templer said.
Musharraf , who took power in a 1999 coup, said in a televised address Wednesday that he supported election authorities' decision to delay the vote due to riots that followed Bhutto's death. The violence killed nearly 60 people and caused tens of millions of dollars in damage.