More than 60 artworks and artefacts at some of Berlin’s best-known museums were smeared with an oily liquid by an unknown perpetrator or perpetrators earlier this month, authorities said on Wednesday.
They are hopeful the apparently random damage can be repaired but said the motive is a mystery.
The works at the Museum Island complex, a Unesco world heritage site in the heart of the German capital, were targeted between 10am and 6pm on October 3, police said.
Investigators said they have watched hours of surveillance camera footage but have not found any obvious sign of anyone applying the liquid.
Christina Haak, the deputy director of Berlin’s state museums, said 63 works at the Pergamon Museum, the Alte Nationalgalerie and the Neues Museum were affected.
There is no thematic link between the targeted works, and “no pattern is discernible” to the approach of the perpetrator or perpetrators, she added.
Friederike Seyfried, the director of Berlin’s Egyptian collection, which is housed in the Neues Museum, said the liquid was oily but not corrosive.
She would not give more specific details of the colourless fluid, citing the ongoing investigation.
Carsten Pfohl, a senior official with Berlin’s criminal police office, said more than 3,000 people visited the Museum Island on October 3, the 30th anniversary of Germany’s reunification.
Complicating investigators’ efforts, most of that day’s tickets were sold on site and only 1,400 personalised tickets were booked in advance.
All of these people have been contacted by email to ask whether they noticed anything untoward.
Police said they initially decided not to go public about the incident out of “tactical considerations related to the investigation”.
On Tuesday night, the weekly Die Zeit and Deutschlandfunk radio broke the story.
Police then called for witnesses to come forward on Wednesday with any accounts of suspicious people or events they noticed on October 3.
It is not clear how the liquid was applied to the works, Mr Pfohl said.
They appeared to have been chosen at random and investigators are inclined to believe a lone perpetrator is responsible, he said, although they are not ruling out multiple perpetrators.
Mr Pfohl added police are investigating “in every direction” but would not participate in local media speculation that conspiracy theorists might be involved.
Germany’s culture minister, Monika Gruetters, strongly condemned the damage to the artworks.
She said in a statement that “there is justified hope that the damage can be repaired” but Berlin’s state museums once again need to answer questions over their security precautions.
In March 2017, robbers broke into the Bode Museum – part of the Museum Island – and made off with a 221lb (100kg) Canadian gold coin known as the “Big Maple Leaf”.
The suspects are believed to have smashed a protective case and then managed to lift the coin out of a museum window before fleeing along a railway track with their haul in a wheelbarrow. It was never recovered.
Ms Haak said the museums’ security is constantly being reviewed and officials are considering how to improve it but “100% security for the objects would mean in principle having to withdraw them from public view”.