A sea of sobbing mourners, some wailing and beating their chests in a wrenching outpouring of emotion, flooded through security checkpoints into the graveyard in rural southern Garhi Khuda Bakhsh for the commemoration. Thick fog had stranded tens of thousands on the roads leading into the area early in the day, prompting authorities to delay the start of the proceedings until 4:00 pm (1100 GMT). Bhutto, 54, was assassinated on December 27, 2007 in a gun and suicide attack at a campaign rally in the garrison city of Rawalpindi, just two months after returning to Pakistan from exile to vie for a third term in power. Her shocking death threw the world's only nuclear-armed Islamic nation into chaos, sparking violence and leading to months of political turmoil that ended in September when her widower, Asif Ali Zardari, claimed the presidency. "In the tradition of a true Bhutto, she faced certain death rather than abandon her principles or the people," Zardari said in a message to the nation to mark the anniversary. "The tyrants and the killers have killed her but they shall never be able to kill her ideas, which drove and inspired a generation to lofty aims," he said, adding that democracy was the only way to fight militancy. The masses travelled by train, bus, truck, car, bicycle and even on foot to mourn the charismatic, Oxford-educated Bhutto, the first woman to lead a Muslim nation and someone hailed in the West as a face of moderation. Some slept Friday night in the open in near-freezing temperatures. Tariq Waseem, a 25-year-old student from southwestern Baluchistan province, walked about 400 kilometres (250 miles) over 10 days with about a dozen friends to be at Saturday's event. But unlike his friends, he walked barefoot. "These are not painful," he told AFP, pointing with pride at blisters covering his soles. "These are a gift from my martyred leader." Local police official Tanvir Odho said about 150,000 mourners had flocked to the area to pay their respects to Bhutto. Ceremonies are expected to culminate with special prayers at 5:20 pm -- about the time Bhutto was attacked. Around 7,000 police and paramilitary rangers have fanned out around the tomb to protect Zardari, who has said he too is a target for extremists like those who killed Bhutto. "We do not rule out any threat and we have done all things possible to maintain peace," senior police official Khadim Hussain Rind told AFP. A special wall has been erected around the mausoleum as part of a raft of precautions taken to safeguard Zardari. Closed-circuit cameras have been installed, and mourners were required to pass through metal detectors. Both Zardari and the United Nations said they hoped a UN investigation would soon be launched into Bhutto's killing. Pakistani and US officials have pinned the blame on Taliban commander Baitullah Mehsud, but he denies any involvement. One year on, Pakistan's reverence for Bhutto continues unabated -- all television networks ran wall-to-wall Bhutto coverage on Saturday and the government has issued a 10-rupee coin and stamps bearing her portrait. Hundreds of vendors did a brisk business selling Bhutto memorabilia -- posters, photographs and recordings of her speeches -- ahead of the ceremony. The government has declared Saturday a national holiday in Bhutto's honour, and events were scheduled nationwide. Candlelight vigils were held late Friday in Rawalpindi and the southern port city of Karachi. Mohammed Amin, a labourer from Pakistani Kashmir, said he had come to Bhutto's grave without fear, despite threats of violence. "My leader died in an act of terror, and so if I am killed in a similar act, it will be an honour for me to join my leader," he told AFP.