The head of the committee charged with purging Iraqi institutions of those linked to the regime of Saddam Hussein has been killed in the Iraqi capital Baghdad, officials said.
Ali al-Lami was shot dead at the wheel of his car in eastern Baghdad by unidentified gunmen, officials said.
Under the de-Baathification policy, Lami banned scores of Sunni candidates from parliamentary polls last year.
Correspondents say he had almost certainly made plenty of enemies.
Entifadah Qanbar, a politician and friend of Lami's, said he was shot dead driving home in what he described as a "well-planned operation".
"He was going from Palestine Street to his house in east Baghdad. His brother was driving. He was followed carefully by a car, then he was intercepted," Mr Qanbar told AFP news agency.
"He was shot in the head with silenced pistols, and pronounced dead in the hospital about 20 minutes after that, at 2000 (1700 GMT) tonight (Thursday)."
The Justice and Accountability Commission (JAC) - which Lami headed from 2004 - was responsible for vetting Iraqis seeking government jobs for connections to Saddam Hussein's Baath Party, which ruled Iraq for decades before it was overthrown in the US-led invasion.
The body was criticised last year after excluding hundreds of Sunni candidates from standing for parliamentary seats in the March elections. Lami ran in the elections himself but was unsuccessful.
In 2008, Lami was arrested by US and Iraqi forces for alleged ties to Iranian-backed Shia militias, and was accused by US officials at the time of being involved in a bombing in Baghdad.
Friends of Lami said they believed Baath party loyalists were behind the assassination.
The shooting is the latest in Iraq's wave of targeted killings against politicians and officials. Although violence in Iraq is down from the peak of the insurgence, almost daily attacks continue.