The gunman who killed three people in the Liege city centre attack also murdered his cleaner before setting out on the massacre.
The body of a woman in her 40s was discovered during a search of Nordine Amrani’s property, officials said.
Police said he killed her, then dumped her body in a warehouse where he had grown cannabis plants and kept a store of weapons.
“It was a cleaning lady. This is how she met him yesterday morning,” prosecutor Daniele Reynders said. “She dies, shot with a bullet in the head.”
Amrani, 33, shot himself after Tuesday’s attack and he was found with grenades still on him.
“What killed him was a shot in the middle of his forehead,” said Ms Reynders.
Two teenage boys aged 15 and 17 died in the attack, while an 18-month-old toddler died later in hospital. A 75-year-old woman initially counted among the dead has been taken off the list, even though she stands virtually no chance of recovering from her injuries.
Beyond the dead and injured, Ms Reynders said 40 people had to be treated for psychological trauma.
It remained unclear what caused the attack. Amrani, who had been jailed for offences involving guns and drugs, had been called in for questioning by police in a sexual abuse case.
Officials said he left his Liege home with a backpack, armed with hand grenades, a revolver and a assault rifle.
He walked alone to a busy central square, then got onto a platform offering a view of the area below, which was bedecked with a huge Christmas tree and crowded with shoppers. He lobbed three hand grenades toward a nearby bus shelter, which serves 1,800 buses a day - the explosions sending shards of glass from the shelter across a wide area. He then opened fire on the crowd. Hundreds fled the square as well as a nearby Christmas market in panic.
Yesterday, a crowd gathered at the Place Saint-Lambert for a minute’s silence at noon, 24 hours after the shooting, lighting candles at the bus stop.