Liege, Belgium (CNN)A man who killed two policewomen and a bystander in the eastern Belgian city of Liege on Tuesday is suspected of killing someone the day before, according to the country's federal prosecutor's office.
Belgium attacker had killed another person the day before
The perpetrator -- named as 31-year-old Belgian national Benjamin H. -- was serving a jail term for theft, violence, drug abuse and insubordination to police, the spokesperson for the Belgian Federal Prosecutor's Office, Eric Van Der Sypt, said Wednesday.
He had been let out of prison on a temporary release, Van Der Sypt said.
According to the terms of his parole, he had been expected to return to jail on Monday night at 7:30 p.m. (2:30 p.m ET) but failed to sign in. Instead, Belgian authorities now also suspect him of committing a burglary and then killing his accomplice.
On Tuesday morning, the man stabbed two policewomen from behind before stealing their service weapons and using them to kill the officers. The attacker then opened fire on a parked vehicle nearby, killing the driver inside.
The gunman later took a woman hostage at a local school before being shot dead by police.
The federal prosecutor's office said Wednesday that the suspect shouted "Allahu Akbar" ("God is greater" in Arabic) several times during the attack -- which they are continuing to investigate as terrorism.
Prosecutors said the exact motive remains unclear but they are continuing to investigate. Also unclear is whether he was acting alone.
Police understand the gunman was in contact with extremist elements between 2016 and 2017 but found no information on any extremist links this year.
The modus operandi of the crime lends credence to the hypothesis that it was a terrorist attack, considering that ISIS online videos often call on their followers to attack police and kill them with their service weapons, Van Der Sypt said.
A toxicology report has been requested on the attacker, he added.
Belgian authorities also faced questions over why a potentially radicalized prisoner was granted temporary release on Wednesday, according to Reuters.
The justice minister, who presides over the prison service, told CNN affiliate RTBF radio he felt "responsible."
"I have to examine my own conscience," Koen Geens said.
Belgium has been on a higher level of alert following a series of terror attacks in the country and neighboring France in recent years. Belgian authorities have previously faced criticism for missing opportunities to stop radicalized nationals who were later identified in the Paris and Brussels terror attacks.
Liege is Belgium's third-largest city, after Brussels and Antwerp, according to the national tourist office. For centuries, it has been an important cultural and industrial center for the country.
In 2011, Liege was also the scene of a grenade and gun attack that left at least five dead and injured more than 100.