Abdul Majid al-Khoei was hacked to death alleged by a mob of supporters of Sadr in the Iraqi holy city of Najaf in 2003. He was the secretary-general of the British charitable Iman al-Khoei Foundation, an organization set up by Shiite Grand Ayatollah Abul-Qassim Khoei after the Persian Gulf war.
Haidar al-Khoei, the son of the slain leader, told London's pan-Arab daily Asharq al-Awsat that the family would take their claims to the international community if Baghdad didn't act on an arrest warrant issued in 2004 for Sadr in connection to the slaying.
"If this does not happen, we will be forced to go to the United Nationals, on the basis that the Imam al-Khoei Foundation has a seat at the U.N. as a non-governmental organization," he said. "We will also go to human rights organizations and the European judiciary."
He added that the family had information to suggest a Sadrist member of Parliament called on authorities to "steer the blame" from the anti-American cleric.
Sadr returned to Najaf this week after living in exile in Iran. He fled Iraq in 2007 after U.S. forces descended on his supporters following post-invasion guerrilla war in the Sadr City slum of Baghdad.
His political party made notable gains in March parliamentary elections in Iraq and were in part responsible for securing a second term for Iraqi Prime Minister Nouri al-Maliki.