Iqbal Raad was killed with two other men as he sat at his desk on Friday. Three gunmen, one carrying a Kalashnikov rifle and the others pistols, ran from the building into a waiting car. Police have made no arrests and no one has claimed responsibility for the murders.

Hundreds of lawyers gathered for Raad's funeral. Sharif himself asked to leave jail to attend the burial but permission was refused.

Sharif's defence team said they would not attend tomorrow's hearing. 'We want a change of venue to Islam abad or Lahore,' said Khwaja Sultan, the leading defence counsel. 'We will not be going to Karachi. It is not safe.'

He said Raad and other colleagues had received telephone threats before the shooting and complained they were given less security than prosecutors in the case.

'We have to queue up to go into court every day alongside the public. Anyone could be amongst them,' he said.

Sultan said he had received one threatening telephone call warning him about his involvement in the case. 'I simply ignored it,' he said.

The murder of his colleague, he said, was probably an attempt to disrupt the trial of Sharif, who was overthrown in a military coup last October. 'There are so many powers interested in sabotaging the case,' he said.

Sharif, his brother Shahbaz and five former senior government officials have been charged with attempted murder, hijacking, kidnapping and terrorism in a case based on the night of the coup. All have pleaded not guilty. They face the death penalty if convicted.