On Monday, police reported the artist duo Elmgreen & Dragset’s national monument in Berlin’s Tiergarten—which honors the fifty thousand gay men who were persecuted during the 1930s and 1940s, thousands of whom were castrated and sent to concentration camps, by the Nazis—had been vandalized with black paint. The act is thought to have been politically motivated, and authorities have begun an investigation to identify the defacers, reports Monopol. Memorial to Homosexuals Persecuted Under Nazism has already been the victim of unknown perpetrators. In 2008, the same year the memorial was unveiled, vandals ripped down fencing around the work and smashed the window through which one could see an image of two men kissing.

“To see such a thing today after all the suffering and horror we had to go through, it is cruel,” said Rudolf Brazda, a survivor of the Buchenwald concentration camp, where he was imprisoned for being gay. The sculpture was unveiled by then-mayor Klaus Wowereit, one of the first openly gay German politicians. Nazi-era laws were in place until 1969 and were used to legally persecute gays in Germany.