Bhutto wrote to President Pervez Musharraf before her assassination on Dec. 27, identifying four members of the civilian-military establishment who should be investigated if she was killed.
Ijaz Shah, head of the Intelligence Bureau (IB), one of Pakistan's three security services, was believed to be one of the people Bhutto suspected of conspiring against her.
Bhutto survived a suicide bomb attack during her homecoming procession through Karachi in October to mark the end of more than eight years of self-exile. At least 139 people were killed in the attack.
Shah, a retired army brigadier regarded as close to Musharraf, held a "farewell meeting" with caretaker Prime Minister Mohammadmian Soomro on Monday.
"He sent his resignation several days back. It's been accepted and yesterday he paid a farewell call on the prime minister," a senior government official told Reuters.
The government controls the IB, whereas the Inter Services Intelligence (ISI) and Military Intelligence are part of the army-dominated military.
Güncelleme Tarihi: 18 Mart 2008, 14:28