The 44-year-old man, named only as Thomas S., was a paid informant for the Berlin criminal police (LKA) between 2000 and 2011, Der Spiegel reported.
He has admitted to having supplied the gang with TNT between the end of 1996 and 1999, during which time he also had a romantic relationship with one of the gang. Although he did not tell his handlers about the explosives, he did give them several tips about where the gang was – but the Berlin authorities failed to pass this on to colleagues who were actively hunting the trio.
Uwe Böhnhardt, Uwe Mundlos and Beate Zschäpe formed a gang calling itself the National Socialist Underground – they were all known figures in the eastern German neo-Nazi scene.
After their explosives were discovered in a garage, the trio went underground and were helped by various other neo-Nazis. They are thought to have killed eight shopkeepers of Turkish origin and one man from Greece in towns across the country, by walking up to them and shooting them in the head.
Police failed to link the killings and rather than considering a far-right background, assumed they were linked to foreign criminals, or even “clan conflicts.”
The NSU are also the top suspects in the 2007 murder of a policewoman who was shot and killed in her car.
The gang carried out bank robberies to fund their secret lives, and the case was only blown open when one of those robberies went wrong and the two men were surrounded by police in a caravan. One shot the other and then killed himself, leaving Zschäpe to allegedly blow up the flat they shared.
She then handed herself in to the police and now faces a range of charges including murder.
Not only was Germany rocked by the presence and effectiveness of a neo-Nazi murder gang in its midst, the entire police and intelligence structures are slowly and reluctantly giving up their secrets.
The authorities have been embarrassed by multiple links to numerous neo-Nazis, many of whom were paid for information. Investigations have also unearthed a host of clues that investigators failed to pass on and which might have led to the gang.
There was also a file-shredding scandal as the parliamentary investigative committee started its work.
Several top intelligence officials including Heinz Fromm, president of the Federal Office for the Protection of the Constitution (BfV), have stepped down over their failure to stop the killings and the botched investigations.
The parliamentary committee only discovered on Thursday that Thomas S. had been an informant for the Berlin LKA – and it was not the Berlin LKA that told them, but the federal prosecutor. This has left the committee infuriated.
It now appears Thomas S. gave them clear hints about how to find the gang three times, Der Spiegel said – between 2002 and 2005, but that none of this information was passed on to colleagues in Saxony actively looking for the trio.
He was “deactivated” as an informant in January 2011. The NSU was uncovered in November 2011 – but it took until March 2012 before the Berlin BKA gave their files on him to the federal prosecutor.
The Süddeutsche Zeitung also reported on Tuesday that the German Military Counter-intelligence Service (MAD) tried to recruit NSU member Mundlos as a mole in Germany's far-right scene during the 1990s. MAD also suppressed the file, despite the parliamentary investigation.