A news conference in Kinshasa has been told Laurent Kabila's assassin was a former boy soldier.
The assassin, named only as Rashidi, had apparently been a follower of Kabila since the 1997 uprising against President Mobutu Sese Seko.
Justice Minister Mwenze Kongolo said the assassin was himself shot dead after the killing.
Mr Kongolo was giving the first official account of Tuesday's shooting of the President of the Democratic Republic of the Congo which happened at the presidential palace in Kinshasa.
"The guard came in and it was natural for Kabila to listen to what he had to say," said Mr Mwenze, explaining why the president had leaned forwards as the gunman opened fire.
"One of the bullets went right behind the ear and came right behind the ribs. I think that's the one that killed him. Two other bullets went in the stomach but were not fatal.
Those are the closest bodyguards that the president had. They are usually armed. The door was open so that air could circulate," he added.
The tentative identifcation of the killer, who shot Mr Kabila in the courtyard of his Marble Palace, cast little light on the motives for his murder. Many observers suspect Mr Kabila was killed as part of a wider plot.
Mr Kabila's 31-year-old son Joseph is to formally sworn in as his successor on Tuesday.