Iraqi researcher Husham Al Hashimi was a hero, Prime Minister Mustafa Al Kadhimi told the murdered man's children as he promised to be their father and find the men responsible.
Al Hashimi, 47, was an authoritative voice on militant groups and local politics who unofficially advised Mr Al Kadhimi. Using pistols with silencers, gunmen killed Al Hashimi on Monday as he parked his car in front of his apartment block in the Zayouneh district of Baghdad.
"Do not cry. Your father was a hero, you'll grow up and become really proud of him," Mr Al Kadhimi told Al Hashmi's four children as he visited their home to pay his condolences.
"The world is proud of him, everyone, whether they are in Iraq or out, they are proud of him because he used to challenge terrorism in order to build a better future for you."
He told the boys that he would be responsible for them, ensuring they got a good education and were supported. "I will be your father and brother," he said.
Mr Al Kadhimi said his friend "embodied the culture of Iraq."
"He was an intellectual, a professional and used to present Iraq in its best form," he said. "He served Iraq by writing. Only the cowardly are afraid of words," he said, in footage released by his office.
Mr Al Hashimi was an Al Rikaby, one of the most prominent Shiite families in the country.
A relative of Al Hashimi told the prime minister that his killers must be caught.
"I will do everything, as much as is in me, to pursue to the killers," Mr Al Kadhimi replied.
Although there is no claim of responsibility, the finger has been pointed at Iran-backed militias whom the researcher criticised vehemently.
The killing is widely seen as a message to Mr Kadhimi, who took office two months ago, and described the militias as a major factor behind failures of Iraq as a state and the organised crime in the country.
Less than a week before his assassination Al Hashimi appeared on TV to criticise Kataib Hezbollah militiamen arrested by the government for attacking US forces. He said Mr Al Kadhimi should not back down after ordering the raid on one of the militia's bases.
But Mr Al Kadhimi released the dozen or so militiamen and Kataeb Hezbollah's spokesman, Mohammed Mohie, described the raid on his group's headquarters as an act of "provocation" and warned of further escalation.
Anti-militia and anti-Iran civil figures were kidnapped and threatened in Iraq after the outbreak of the mass protest movement in October that demanded the removal of the entire political class.
Hundreds were abducted or disappeared and more than 700 protesters killed by security forces and militias.
As he walked the entrance of the apartment building where Al Hashimi lived, Mr Al Kadhimi passed by posters put up by members of the protest movement, mourning Al Hashimi – who supported the people's demands – as one of their own.
One was signed by the teams of tuk-tuk motor taxis that have been ferrying wounded or dead demonstrators from the front lines of protests. Others were erected by organisers of the main sit-in at Baghdad's Tahrir Square.
"To heaven, brave man," a caption under Al Hashmi's picture read.