Pakistani police are questioning three men about their possible involvement in the attack on former Prime Minister Benazir Bhutto.
An investigator says the men are linked to a vehicle that police believe was used by someone who threw a grenade at Ms. Bhutto's motorcade. The grenade brought the convoy to a halt, and seconds later, police say, a suicide bomber blew himself up in the midst of a huge crowd cheering Ms. Bhutto's return to Karachi.
The blast late Thursday killed nearly 140 people and wounded hundreds of others.
The police investigator says the three men were detained in the southern part of Punjab province, Pakistan's most populous area, and brought to Karachi for interrogation.
Police also have released a photograph of the suspected suicide bomber, who has not yet been identified. The photo showed the man's severed head lying on a sheet.
In several neighborhoods of Karachi on Saturday, people burned tires and threw rocks at passing cars to protest the attack, which turned Ms. Bhutto's joyfyul homecoming celebration into a scene of carnage and suffering.
Ms. Bhutto has told reporters on Friday she had been tipped by a foreign government that four assassination teams were planning attacks as soon as she returned to Pakistan from eight years in self-imposed exile.
While mourning the casualties, the 54-year-old former prime minister said she cannot let such attacks set back her political efforts in Pakistan.
A top Taliban commander has denied any involvement in Thursday's carnage, and no other group has claimed responsibility for the attack, which has drawn strong condemnation worldwide. President Pervez Musharraf has promised a thorough investigation.