On Thursday, a police spokesman said several people had come forward with information on the incidents, which occurred at three museums on the UNESCO-protected Museum Island on October 3, but were only made public this week.

It remains unclear who was behind the attacks, what the motive was, and how exactly the colourless, oily substance was applied to 63 artworks and antiquities, including ancient Egyptian sarcophagi.

“The diagnosis is out, now we start the individual therapy,” said Christina Haak, deputy director general of the German capital’s state museums.

The sum total of damages in the unprecedented spree, which took place in the New Museum, the Pergamon Museum and the Old National Gallery, is not yet clear.

Haak told dpa that the museums are considering tougher security measures. When asked whether this could include bag checks such as those at Berlin’s Jewish Museum, she said: “We are taking everything into consideration.”

Haak would not be drawn on media reports that the attacks could be linked to a far-right conspiracy theory in which the Pergamon Museum is said to be a house of Satanism.

In comments to the RBB broadcaster, Hermann Parzinger, president of the The Prussian Cultural Heritage Foundation which runs Museum Island, lamented the vandalism and said: “What is going on in our society?”