Authorities in western Germany have suspended 29 police officers suspected of sharing far-right propaganda in WhatsApp groups, at least two of which were active for several years, a top security official said Wednesday.

Investigators searched 34 locations, including police stations and private apartments in the Ruhr industrial region, said Herbert Reul, the interior minister of North Rhine-Westphalia state, Germany’s most populous.

The material that was shared included “the most foul and repugnant neo-Nazi, racist and anti-refugee agitation,” said Reul, who added that the case left him “speechless.”

The offending images included pictures of Adolf Hitler and swastikas, a fictional depiction of a refugee in the gas chamber of a concentration camp and another mocking the shooting of black-skinned people, Reul added.

The material was exchanged in at least five WhatsApp groups used entirely or largely by police officers, Reul said. One of those groups apparently was set up in 2012, and the one that contained the most images, in 2015. The most recent message was sent on Aug. 27.

Most of the officers allegedly involved worked at some point at the same police precinct in Muelheim an der Ruhr, Reul said. All 29 were suspended with immediate effect on Wednesday, and disciplinary proceedings opened.

“We have to ask unpleasant questions of ourselves,” Reul said. “Who knew about this? Why was this tolerated for years? By whom?”

The case puts a spotlight on neo-Nazi ideology in Germany’s police forces, an issue that senior security officials had previously downplayed even as they warned of the growing threat of far-right violence in recent years.

In July, Germany’s top security official at the federal level, Horst Seehofer, rejected calls for an investigation into the extent of racial profiling by the police, insisting that there was “no structural problem.”