What happened
The NSU (National Socialist Underground) killed nine people of Turkish and Greek heritage between 2000 and 2006, plus a German policewoman in 2007, in a pattern investigators nicknamed the 'Döner murders' — a name that itself reflected the racialised assumptions driving the investigation. Police repeatedly treated victims' families as suspects, pursued theories involving the victims' own alleged criminal connections, and did not seriously investigate organised far-right terrorism as the motive for a decade.
The cell was not uncovered by police work. It came to light in November 2011 when two of its members died in an apparent murder-suicide after a botched robbery, and a third member turned herself in. Only then did investigators discover the group had been operating with a network of far-right sympathisers for over a decade.
German domestic intelligence (the Verfassungsschutz) had informants embedded in the far-right milieu that produced the NSU, and information that could have connected suspects to the killings was, according to parliamentary inquiries, not shared with police investigating the murders. This was not merely an investigative failure of imagination — it was a security state that had eyes on the far-right scene and did not use them to stop it killing.