Unidentified perpetrators have scrawled graffiti over posters with photographic portraits of survivors of the Buchenwald concentration camp in Weimar, according to police.

A police spokesperson said on Thursday that a charge of damage to property had been filed. The police assume that the act was politically motivated. The graffiti on the two portraits would be removed as soon as possible, they said.

The pictures are part of an open-air exhibition in Weimar called “The Witnesses”, which shows large-format portrait photographs of former prisoners of the former Nazi concentration camp Buchenwald. Panels of the exhibition have also been defaced in the past.

The organisers of the Jewish-themed Achava Festival, which regularly takes place in Weimar, posted about the case on Twitter on Wednesday evening and asked for witnesses to come forward. “Today two photographs were smeared and thus desecrated!” they tweeted.

In all, 280,000 people were imprisoned in Buchenwald during the Nazi era, with 56,000 losing their lives there.