Bhutto said there were two attackers in the deadly bombing, and that her security guards found a third man armed with a pistol and another with a suicide vest. Ahead of her arrival, she said, she was warned suicide squads were dispatched to kill her.
CBS News' Farhan Bokhari reported that Bhutto's return to Pakistan had been preceded by intelligence reports suggesting that members of Al Qaeda were planning to target her.
According to CBS News correspondent Sheila MacVicar, even before her return, Bhutto was so convinced there would be an assassination attempt that she sent the names of three suspected conspirators to Pakistan's president and a senior American journalist, Arnaud de Borchegrave.
The message read, "I have been informed that Baitur Massoud, an Afghan; and Hamza bin Laden, an Arab; and a Red Mosque militant have been sent to kill me."
Upon her arrival on Thursday, she set aside the security plan to be visible only from behind a bullet proof glass and instead chose to stand on an elevated platform, raising objections from Karachi police officials who said Bhutto had compromised her security.
The first blast came from a suicide bomber who got through lines of police protection. A second, bigger bomb transformed the streets into a burning hell of burning bodies, some with terrible injuries, others simply dead from the explosion, MacVicar told The Early Show.
Bhutto survived unscathed, but the back-to-back explosions that went off near a bulletproof truck in which she was riding turned her jubilant homecoming parade through the city streets into a scene of blood and carnage, ripping victims apart and hurling a fireball into the sky. The attack shattered the windows of her truck. She appeared dazed afterward and was escorted to her Karachi home.
"There was one suicide squad from the Taliban elements, one suicide squad from al Qaeda, one suicide squad from Pakistani Taliban and a fourth - a group - I believe from Karachi," she said.
Baitullah Mehsud, a top militant leader on the unstable Afghan border, threatened this month to meet Bhutto's return to Pakistan with suicide attacks, according to local media reports. An associate of Mehsud, however, denied Taliban involvement.
Bhutto said her guards prevented more carnage.
"They stood their ground, and they stood all around the truck, and they refused to let the suicide bomber - the second suicide bomber - get near the truck," she said.
"We believe democracy alone can save Pakistan from disintegration and a militant takeover," she told a news conference. "We are prepared to risk our lives and we are prepared to risk our liberty, but we are not prepared to surrender our great nation to the militants."
She did not blame the government, but said it was suspicious that streetlights failed after sunset Thursday when her convoy was inching its way through the streets of Karachi. She said attempts to reach the national security advisor to have the lights restored were unsuccessful - phone lines were also apparently down.
"I'm not accusing the government but certain individuals who abuse their positions and powers," she said. "We were scanning the crowd with the floodlights, but it was difficult to scan the crowds because there was so much darkness."
Pakistan did everything it could to protect Benazir Bhutto on her homecoming, a top government official insisted on Saturday, dismissing accusations that officials may have been complicit in the attack.
"I think we should stop playing blame games. The government provided the best possible security to her," Deputy Information Minister Sen. Tariq Azim told The Associated Press. "The trauma of the attack has made them say things which probably in coolness of things they will not repeat."
"Peoples names have been mentioned and names have been hinted at without giving any reason or without giving any proof of their involvement, and that is unfair," he said.
Bhutto said the next attack against her would target her homes in Karachi and her hometown of Larkana, using attackers posing as supporters of a rival political faction.
She blamed the attack on militants trying to quash democratic reforms.
The attack - one of the deadliest in Pakistan's history - bore the hallmarks of militants linked to pro-Taliban warlord Baitullah Mehsud and al Qaeda, according to Ghulam Muhammad Mohtarem, the top security official in Sindh province, where Karachi is located. He suggested that Bhutto's camp had gotten carried away celebrating her return after eight years in exile, and had not taken the need for security seriously.
"We were already fearing a strike from Mehsud and his local affiliates and this was conveyed to the (Bhutto's Pakistan's) People's Party but they got carried away by political exigencies instead of taking our concern seriously," Mohtarem said.
President Gen. Pervez Musharraf, the nation's leader, phoned Bhutto Friday to express his shock and profound grief over the bombing and prayed for the former premier's safety and security, his spokesman said.
"The president and Ms. Bhutto both expressed their unflinching resolve to fight this scourge of extremism and terrorism. They also agreed that there was a need for the entire nation to unite in order to rid the country of this menace of suicide bombings, terrorism and extremism," Qureshi said.
Musharraf resolved to "bring the perpetrators of this heinous crime to justice."
There was no claim of responsibility for the attack, which shed new uncertainty over Bhutto's talks with Musharraf and possible plans for a moderate, pro-U.S. alliance. Leaders of her Pakistan People's Party were meeting at her Karachi residence Friday, and Bhutto was expected to hold a news conference afterward.
Bhutto returned to Pakistan under a controversial deal with the military leader Musharraf. He has set aside corruption charges against her and supposedly agreed to leave the military and become a civilian politician, reports MacVicar.
Mohtarem said nuts and bolts and steel balls packed around the explosives had made the bombing so deadly. He said it was impossible to prevent more such attacks.
Local hospitals have reported 136 dead and and 250 wounded, Karachi police chief Azhar Farooqi said that 113 people died, including 20 policemen, and that 300 people were wounded. It was not immediately possible to reconcile the differing death tolls.
Interior Minister Aftab Khan Sherpao said 18 police died in the attack, as two police vehicles on the left side of Bhutto's truck bore the brunt of the blast.
Police collected forensic evidence - picking up pieces of flesh and discarded shoes - from the site of the bombing. The truck was hoisted away using a crane. One side of the truck, including a big portrait of the former premier was splattered with blood and riddled with shrapnel holes.
He said authorities had done everything possible to protect the huge gathering of Bhutto supporters marking her return, but noted that electronic jammers fitted to the police escort vehicles were ineffective against a manually detonated bomb.
Karachi, which lies in the far south of Pakistan but has been buffeted by militant attacks in recent years, was quiet Friday. Schools were closed and traffic was thin, with city residents wary of venturing out.
Unrest broke in two districts but did not appear serious. Hundreds of Bhutto supporters hurled stones at vehicles and shops during a funeral procession for two victims, forcing police to cordon off the area. Elsewhere, Bhutto supporters ordered shops to close and burned tires in the road.
On Saturday, a bomb ripped through a bus parked at a terminal in southwestern Pakistan on Saturday, killing seven people and wounding six others, police said.
The explosion occurred in Dera Bugti, a tribal town in insurgency-hit southwestern Baluchistan province, police officer Raja Bashir said.
Bhutto had flown home Thursday to lead her Pakistan People's Party in January parliamentary elections, drawing cheers from crowds that police put at 150,000. She has ambitions to win a third term as prime minister.
The throngs reflected Bhutto's enduring political clout, but she has made enemies of Islamic militants by taking a pro-U.S. line and negotiating a possible alliance with Musharraf.
It remained unclear what impact the attack could have on reconciliation efforts between the two rivals: whether it could stiffen their resolve to fight militancy together or strain already bad relations between Bhutto and the ruling party supporting Musharraf.
Bhutto's husband, Asif Ali Zardari, said on Dawn News television that he suspected that "elements sitting within the government" who would lose out if Bhutto returned to power were involved in the attack. In the past, Bhutto has accused conservatives in the ruling Pakistan Muslim League-Q party and the security services of secretly supporting religious extremists.
Bhutto has a long list of enemies. People say Musharraf has rogue elements within his intelligence services and they tried to kill her, Sky News reporter Tim Marshall told The Early Show.
Upon arriving from Dubai, she told AP Television News she was fighting for democracy and to help this nuclear-armed country of 160 million people defeat the extremism that gave it the reputation as a hotbed of international terrorism.
"That's not the real image of Pakistan," she said.
Leaving the airport, Bhutto refused to use a bulletproof glass cubicle that had been built atop the truck taking her toward the tomb of Pakistan's founding father, Mohammed Ali Jinnah. An AP photographer who saw the cubicle of the wrecked truck said it appeared to have shrapnel holes from the bombing.
Manzur Mughal, the Karachi police officer in charge of the investigation said detectives had established that the same young man who threw the grenade blew himself up 22 seconds later next to the truck.
Pakistani television showed footage Friday of what it said was the severed head of the suspected suicide bomber - an unshaven man in his 20s with curly hair and green eyes.
The attacker's head was taken to a forensic lab to try to identify him, Mughal told The Associated Press.
Bhutto had paved her route back to Pakistan through negotiations with Musharraf, a longtime political rival despite their shared liberal values. Their talks yielded an amnesty covering the corruption charges that made Bhutto leave Pakistan.