The man who shot dead two police officers and a civilian in the Belgian city of Liège had killed someone the night before the attacks, the country's interior minister says.
Jan Jambon said the gunman, named as Benjamin Herman, had murdered a man - a former prisoner - he met while in jail, reports BBC.
Prosecutors say they are treating the attacks as "terrorist murder".
The gunman also took a female cleaner hostage at a school before being killed by police.
Officials said the 31-year-old man had shouted "Allahu Akbar" several times during the attack.
He was let out from prison on temporary release on Monday where he had been serving time for theft and drug offences. Local media report that he may have been radicalised while in jail.