Liege, an industrial city close to the German border in a French-speaking region, was the scene of a shooting in 2011, when a gunman killed four people and wounded more than 100 others before turning the gun on himself.
An investigation has been launched into the incident, including the circumstances surrounding the attacker's release from prison, Jambon said.
According to federal justice minister Koen Geens, Herman had been on penitential leave 25 times, serving a 12-year sentence for a variety of offences, without a problem to date.
"The one responsible for the shooting was shot dead", Liege's mayor office said later. Local media report that he may have been radicalised while in jail.
The country's Interior Minister, Jan Jambon, told Bel RTL radio on Wednesday that Mr Herman was also behind the murder of his former cellmate, Michael Wilmet, who was bludgeoned to death on Monday night.
Roggen said the attack was being treated as terrorism given the way Herman acted, which she said resembled Islamic State of Iraq and Syria (ISIS) calls via video to attack police with knives and steal their weapons, the fact that he yelled Allahu Akbar and was in contact with radicalized people. He said Belkacemi was the mother of 13-year-old twin daughters who earlier lost their father, also a police officer.
The attacker then ran into a school and took a woman hostage inside.
Belgium's deputy prime minister Alexander de Croo said: "Everyone in Belgium is asking the same question: how is it possible that someone convicted for such serious acts was allowed to leave prisons?"
Liege prosecutors' spokesman Philippe Dulieu said the man crept up on the two officers from behind, before stabbing them several times.
State broadcaster RTBF identified the suspect as Benjamin Herman.
When asked about the report that the attack was terror-related, Liege city hall Michel Firket said: "I know nothing formal about that".
Herman allegedly stabbed two female police officers from behind before taking their handguns and fatally shooting them.
Imaankaf Darifa, the hostage, told the Associated Press she tried to keep him away from the children at the school.
Two other officers received injuries to their arms before the attacker was shot dead, prosecutors said.
The assailant has since been "neutralized", a spokesperson from the Liege prosecutor's office told CNN.
Despite the potential terrorism link, Belgium's crisis centre said it saw no reason to raise the country's terror threat alert for now.
RTBF said the attacker had a history of minor criminal convictions but was not on a list of possible violent extremists.
In this undated handout provided by the Liege Police Department on May 30, 2018, Liege police officers Soraya Belkacemi, left, and Lucille Garcia, right, are seen in their uniforms.
The attack has shaken Belgium, where police and military have been working overtime to guard public buildings since coordinated suicide attacks on Brussels Airport and the city's subway system killed 32 people and injured hundreds on March 22, 2016.