Gunmen on a motorcycle on Friday shot dead a prosecutor investigating the 2007 assassination of former Pakistani Prime Minister Benazir Bhutto, one of the most shocking events in the country's turbulent history.

Police sources said Chaudhry Zulfikar was shot in his car after he left home and headed to a hearing in the case, a reminder of Pakistan's instability just a week before general elections.

"He was killed by unknown gunmen. Twelve bullets were fired," said a police source.

Zulfikar was also the prosecutor investigating the 2008 attacks on India's commercial capital, Mumbai, in which 166 people were killed. India said militants based in Pakistan were behind the three-day rampage.

The attack on Zulfikar left glass and blood stains on the front seats of his car.

Security expert Amir Rana said Zulfikar was probably a marked man because he had been prosecuting militants who were jailed in connection with Bhutto's death, or other cases.

Bhutto's assassination is shrouded in mystery.

She was killed in a gun and suicide bomb attack carried out by a 15-year-old boy after an election rally in the city of Rawalpindi, weeks after she returned to Pakistan from years in self-imposed exile.

A report by a U.N. commission of inquiry released in 2010 said any credible investigation should not rule out the possibility that members of Pakistan's military and security establishment were involved.

Bhutto was a fierce critic of Pakistan's Taliban and Islamist groups that had been patronised by elements of Pakistan's military. She was deeply mistrusted by the security establishment.

Speculation has lingered that Bhutto was the victim of a plot by allies of General Pervez Musharraf, the president at the time, who did not want her to come to power.

The killing of the prosecutor comes days after a Pakistani court put Musharraf on a 14-day judicial remand for charges of failing to provide adequate security for Bhutto before her assassination.

The former army chief, who has always denied responsibility for Bhutto's death, returned to Pakistan in March after nearly four years of self-imposed exile to contest the May 11 general election. But has since been banned from politics for life. – Reuters