Not in the USA, but Germany. The NSU-complex.
NSU stands for NationalSocialist Underground, a group of 3 people who murdered 10 immigrants over the last decade. They got uncovered in Nov 2011 because -supposedly- 2 of them suicided and the third , a women, turned herself in.
The cover up is about the role of police and our domestic intelligence service, the BfV. (BfV= State Office for the Protection of the Constitution ) To sum it up, the Police did not even think about a hate crime, but assumed they where killed because they where part of the mafia, not bothering investigating further.
But the role of the BfV is much worse. Thank god some parliamentary enquiry committees have been put in place, one on federal, and one on state level that brought some things onto the surface. I dont even know where to start. Maybe that AFTER the group got known, hundreds of documents had been shreddered by the BfV supposedly by "mistake". Nobody belives that. Not even the MPs. Despite the documents beeing destroyed, the committees found out a lot of shit. For example, the BfV had a bunch of informants very close to the NSU, making it unbeliveable that they did not know about them. In 1999, before most of the murders took plase, some investigators found them, and send the SEK (similar to SWAT) to arrest them, but they where denied to act out the operation, triggering massive complaint from members of the SEK. It became known that the BfV interviend several times after that, succesfull avoiding an arrest. During one of their murders, an agent of BfV was at the scene, in private, supposedly not noticing anything. It became known that the agent held deep national and racist belives, called " Litte adolph" in his hometown. Thats not everything, but i stop here know.
Overall, one committe concluded that : " the mistakes done by BfV where so massive that it has to be considered as intentional" The picture that is shown is one of an Intelligence service that meddles with Neonazis, to uphold its existence authority, accepting the deaths of people as outcome of their actions. Together with the other service, BND breaking the constitution on a daliy basis by partnering with the NSA, my trust and the trust of many others in our Intelligence services is long gone.