A gunman who killed three people at a Jewish museum in Belgium was “cold-blooded and very determined”, officials said today, leading some security experts to suggest that he may have been a hitman rather than an anti-Semitic “lone wolf”.

An Israeli couple and a French woman were killed in the shooting in Brussels city centre on Saturday. A Belgian man remained critically wounded last night.

Police have released a 30-second video clip from security cameras which shows a man in a dark cap, sunglasses and a blue jacket enter the building, take a Kalashnikov assault rifle out of a bag and shoot into a room before calmly walking out.

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“The footage shows an individual who acts in cold blood and is very determined,” said Ine Van Wymersch, a spokeswoman for the Brussels prosecutor’s office. In a sign of the severity of the case, she said it was being handing over to federal investigators. “The identity and nationality of the victims is an additional reason to hand the case to the federal level,” Ms Van Wymersch added.

Prosecutors said they were studying all scenarios and would not speculate about the gunman’s identity or motive. But some terrorism and security experts said the way in which the assailant carried out the killings suggested planning and execution by a specialist.

Edwin Bakker, professor at the Centre for Terrorism and Counter-terrorism at Leiden University in the Netherlands, said no group had claimed responsibility for the attack, suggesting it was not terrorism. “People use the word terrorism very quickly but when I saw the images I thought this is a hitman,” he said.

One of the Israeli victims, Emmanuel Riva, had formerly worked for Nativ, a government agency that played a covert role in fostering Jewish immigration from the former Soviet Union, an Israeli official said. Along with Israel’s foreign intelligence agency, Mossad, and its domestic security equivalent, Shin Bet, the Nativ agency was under the authority of the Prime Minister’s office.

Miriam Riva, his wife, also once worked for the Prime Minister’s office, the official said without elaborating.

Friends of the couple said they both worked as accountants in government service.

Other analysts dismissed the notion that this was a contract killing and said it was more likely to be a random attack on Jews.

Reuters