Baghdad, Iraq (CNN) -- Saddam Hussein's cousin Ali Hassan al-Majeed, also known as Chemical Ali, was sentenced to death Sunday for involvement in a poison gas attack that killed about 5,000 Iraqis in 1988, an official with the Iraqi High Tribunal said.
The attack on the village of Halabja, which earned al-Majeed his nickname, was part of the Anfal campaign, in which the Saddam regime killed at least 100,000 Iraqi Kurds.
Al-Majeed has already been sentenced to death three times -- once for the Anfal campaign, once for his role in putting down a Shiite uprising against Saddam Hussein in 1991, and a third time for his part in putting down a Baghdad revolt in 1999.
Estimates of the Shiite death toll in the 1991 rebellion range from 20,000 to 100,000. Al-Majeed was convicted of playing a key part in the slaughter during the revolt in southern Iraq that followed the 1991 Persian Gulf War.
His execution has been delayed for political rather than legal reasons.
Sultan Hashem, one of the co-defendants in the Anfal case, is a prominent Sunni leader who is considered a key player in efforts to reconcile the country's once-dominant Sunni community with the Shiite majority that now wields political power.
Iraq's Sunni Arab Vice-President Tariq al-Hashimi has so far refused to sign Sultan Hashem's execution order -- delaying the execution of al-Majeed and another defendant as well.
Iraqi law requires all three members of the Iraqi presidency council -- the president and two vice-presidents -- to sign execution orders. It does not say what happens if they do not sign.