"The regime has lost all credibility. Neither a domestic inquiry nor vague foreign involvement ... would lay to rest the lingering doubts and suspicions."
A new videotape of Bhutto's assassination aired on television in Pakistan has raised further questions about the official account of the attack.
"The cameraman manages to capture Benazir Bhutto minutes before the bomb blast," Al Jazeera's Sohail Rahman said from Islamabad.
"But as he loses his focus and tries to find Bhutto in the vehicle she's not there, then a second later the bomb blast goes.
"So it does throw into doubt the government's version of whether she did hit her head as a result of the shockwave of that blast."
Musharraf has blamed an al-Qaeda-linked group for the attack on Bhutto in Rawalpindi, but many Pakistanis are suspicious that Bhutto's other enemies, perhaps in sections of the security agencies, were involved.
In fact, in a report on Bhutto's murder, the Brussels-based International Crisis Group called on the US - of which Musharraf is a close ally - to recognise him as "a serious liability, seen as complicit in the death of the popular politician [Bhutto]".
Robert Templer, the group's Asia director, said in a statement accompanying the report: "It is time to recognise that democracy, not an artificially propped-up, defrocked, widely despised general has the best chance to provide stability.
"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," he said.
Meanwhile, there have been renewed calls for Musharraf to step down as president before parliamentary elections, which on Wednesday were delayed until February 18.
"Free and fair polls are impossible under his leadership," Javed Hashmi, a senior member of Nawaz Sharif's opposition party, said.
"Such a thing is unthinkable if he is there."
Both main opposition parties criticised the postponement but said that they would still take part.
They have also demanded better security for their candidates during the election campaign.
"We would like the government to provide foolproof security to Sharif, including a bulletproof vehicle," Ahsan Iqbal, a spokesman for his Pakistan Muslim League-N, said.