It was 2 a.m. on a Tuesday when the raid began at the Eyewitness War Museum in the town of Beek, the Netherlands.

First, a group of thieves teased open the museum’s front gate.

“You can see it on our cameras,” said Wim Seelen, the museum’s director.

But then, they disappeared.

An hour later, the burglars returned in several estate cars. In a scene reminiscent of a heist movie, they spread out tires across the highway that runs past the museum to create a roadblock, and they parked a fake police car beside it, so it looked official.

Over the next five minutes, the group — maybe 12 people in total, Seelen said — battered down the museum’s front door, broke display cabinets and took what they’d come for: nine mannequins wearing rare Nazi uniforms. The outfits included one worn by Hitler’s personal chef, and another by a high-ranking member of the SS.

The robbers took other items of World War II memorabilia, Seelen said, with the haul worth about $1.5 million in total.

“It was done with military precision,” he added.

The museum’s alarms went off, but the police — held up by the roadblock — arrived too late to catch anyone.

“Of course, I’m terrified it will happen again,” Seelen said.

The Aug. 4 raid in Beek was only the most dramatic in a string of recent robberies from World War II museums in Europe, and the burglaries are spreading panic among similar institutions.

Since March, four museums in the Netherlands and Denmark have been broken into, and memorabilia, including Nazi uniforms, has been stolen. The most recent raid took place Nov. 3, when robbers broke through a window at the German Museum North Schleswig, in southern Denmark, and made off with three mannequins in Nazi outfits.

Administrators from all four of the burglarized institutions said they believed the thieves were acting on the orders of collectors looking to get their hands on rare Nazi memorabilia. But they were uncertain whether the robberies were carried out by the same group, or were simply part of a worrying trend.

Officers of the Dutch and Danish police said in telephone interviews that they had no suspects in any of the robberies but were looking for patterns.

Richard Bronswijk of the Dutch police’s art crime unit said his team had two theories: that wealthy collectors in Russia or Eastern Europe had ordered the robberies, or that they were undertaken by supporters of the far right. The second theory was less likely, he added, “as those guys don’t have much money, and like to buy replicas.”

The raid at the Eyewitness War Museum was incredibly professional, he said.

“They were really like ‘Ocean’s Twelve,’ ” he added, referring to the Hollywood heist movie.

The Netherlands and Denmark, which were both occupied by Nazi Germany during World War II, have numerous small, private and state-funded museums devoted to the history of that conflict. Many have memorabilia including weapons and dioramas depicting scenes from the war, with mannequins in original uniforms.

Many Dutch museums have taken rare items off display or improved their security systems in response to the recent robberies. The Arnhem War Museum has installed anti-tank barriers at its entrance, “so people can’t come with a big truck,” said Marina Moens, one of its owners.

Concern is growing in Denmark, too.

“I’m sure every museum’s taking precautions,” said Henrik Skov Kristensen, director of the Froslev Camp Museum. “But if someone’s determined to do something like this, they will.”