The break-ins at a museum in Beek in August and Ossendrecht in the southern Netherlands two weeks ago prompted a nationwide security review of World War Two museums, said Janneke Kennis, who works at a similar museum in Overloon.
"We don't think they were stolen to sell openly online, because the weapons are numbered and are so unique and rare that they would immediately be recognized," Kennis said.
The thieves were well prepared and appeared to have taken items ordered for private collections, she said.
"They probably scouted the museums to see what they needed to break in, made a list and carried it out very professionally," she said.
At the Eyewitness War Museum in Beek, several vehicles were used in August to get away with the most valuable parts of the collection, estimated to be worth around 1.5 million euros, after burglars forced the gates and rammed the front door.
Years in the making, the collection of 150 costumed characters displayed in dioramas told the story of a German parachutist named August Segel.
At the Ossendrecht museum, thieves cleared out nearly the entire collection, including hundreds of thousands of euros worth of SS uniforms, daggers, helmets, emblems, caps, parachutes, firearms and binoculars.The Overloon museum has since returned to their owners a number of pieces that were on loan, including a one-of-a-kind list of 1,500 victims of the Auschwitz death camp, because they were considered too valuable to keep on public display given the recent break-ins.