Belgian police are appealing to the public to help identify a suspect in the fatal shooting of three people at the Jewish Museum in Brussels.
They have released CCTV footage of the suspect walking into the museum, shooting through a door with an automatic rifle, before walking away.
An Israeli couple in their 50s and a French female employee of the museum were killed in the attack on Saturday.
Unconfirmed reports suggest a fourth person has died from his injuries.
Police have launched a nationwide manhunt for the suspect, who is believed to have parked a car outside the museum before entering, firing and quickly leaving the scene.
Security has been stepped up at Jewish sites across Belgium in the wake of the attack.
The suspect's face is partially hidden by a dark baseball cap in the footage released. A body can be seen in the doorway of the museum. Police described the suspect as of medium height and athletic build.
Earlier, deputy prosecutor Ine Van Wymersch appealed to the "whole population to help identify this person".
The gunman "probably acted alone, was armed and well prepared", she said, adding that all options were open regarding a motive.
The victims were struck by bullets in the face or throat, the prosecutor's office said.
AFP news agency reports that a Belgian man, who was critically wounded in the attack, has succumbed to his injuries.
Several officials have said the shooting appeared to be an anti-Semitic attack.
Belgian Foreign Minister Didier Reynders, who was one of the first people to arrive at the scene, said: "You cannot help think that when we see a Jewish museum, you think of an anti-Semitic act. But the investigation will have to show the causes."
Israeli Prime Minister Benjamin Netanyahu and French President Francois Hollande have both condemned the killings.
Pope Francis, on a visit to Israel, said he was deeply saddened by "this criminal act of anti-Semitic hatred" in Brussels.
Mr Hollande said there was no doubt about the "anti-Semitic character" of the attack.
His comment came hours after two Jewish men were beaten as they were leaving a synagogue in Creteil, 13km (8.1 miles) south-east of Paris on Saturday night.
The attack on the Jewish Museum happened at around 15:50 local time (13:50 GMT) on Saturday in the busy Sablon area of Brussels, which was hosting a three-day jazz festival.
One person was detained after he drove away from the museum around the time of the attack, but Belgian police say the man has been released and is being treated as a witness.