The governor of Pakistan's Punjab province was shot dead by a member of an elite security force on Tuesday, as he was leaving his Islamabad home. The alleged killer was part of his security detail.
Governor Salmaan Taseer may have been shot dead for his role in trying to get a reprieve for a woman given a life sentence under blasphemy laws, officials suspect.
The fear is that the killer could be linked to extremist militant groups.
An intelligence official who interrogated the suspect, identified as Mumtaz Qadri, told the Associated Press that the guard boasted about the assassination, saying he was proud to have killed a blasphemer.
Taseer's killing is the most high-profile assassination of a political figure in Pakistan since the killing of Benazir Bhutto in 2007. He was a member of Bhutto's Pakistan People's Party.
In a nation-wide strike on Friday, religious parties had called for the death sentence against Taseer for what they called his role in promoting blasphemy against the Prophet. But security forces had played down the threat.
The murder of Taseer, governor of Pakistan's most populous and politically important province, has shocked a nation already facing political uncertainty with prime minister Yusuf Raza Gilani's alliance government losing majority.
Taseer was also a close ally of President Asif Ali Zardari.