Scores of authors, artists, academics and activists have lashed out at German authorities, accusing them of covering-up racist murders, and calling for new inquiry into the so-called "NSU" killings and the dissolution of the domestic intelligence agency, the BfV, in a demonstration in Berlin on Tuesday in front of the office of the representative of the state of Hessen, where about 20 people protested against alleged links between BfV agents and far-right extremists which have gathered prominence amid ongoing investigations into the killings by the National Socialist Underground group, or NSU, of eight Turkish immigrants, a Greek worker and a German policewoman between 2000 and 2007.A group of 40 prominent signatories signed a statement read out at the rally, which said: "The NSU scandal is one of the biggest political scandals in Germany's post WWII history. "For many years the NSU carried out its murders throughout Germany, apparently under the surveillance of the domestic intelligence agency."They blamed the Prime Minister of Hessen, Volker Bouffier, and the domestic intelligence BfV for hindering deeper investigations into the allegations."We are demanding the dissolution of the domestic intelligence agency. The Prime Minister, Volker Bouffier, should immediately resign. The contacts between the domestic intelligence agency and those extremists close to the NSU should be completely investigated," they said.Frank Spilker, singer of the Hamburg based group Die Sterne, International Relations Professor Ulrich Brand from the University of Vienna and authors Michael Wildenhain and Thomas Meinecke had signed the joint the statement, which called for a comprehensive investigation into the alleged links.Professor Juliane Karakayali, a sociologist known for her studies on immigration and racism, photo artist Ute Langkafel, artist Natascha Sadr Haghighian and film director Dorothee Wenner were also among the signatories. The NSU carried out its deadly seven-year killing spree apparently without arousing the suspicions of the German police or intelligence services.The signatories said that recent revelations unveiled in the state of Hessen had shown ties between the members of the BfV and far-right extremists.They said in a joint statement: "Recent reports revealed strong indications that there had been ties between the right-wing terrorist network and the domestic intelligence in the state of Hessen."When the 21 year old Halit Yozgat was killed by the NSU in his internet-café in Kassel in 2006, the domestic intelligence spy Andreas Temme was there. There are indications that it was not a coincidence.""The tapped telephone conversations of Temme and one of his informants from the neo-Nazi organizations show that they knew about the murder beforehand," they said.Anti-racist activists who supported the joint statement had organized the demonstration on Tuesday.On a fence surrounding the building, they hung a banner carrying the slogan: "Justice for Halit Yozgat, Bouffier resign!"Some demonstrators carried banners saying "State must end cover-up of NSU murders" and "NSU is financed, sheltered by the domestic intelligence".Halit Yozgat was the ninth victim of the NSU. The domestic intelligence agency at the time ruled out at any "far-right motive" behind the murder, as it had done so in eight previous murders, saying it instead suspected immigrant mafia groups, drug gangs and illegal political groups.Many questions related to the NSU's murders are yet to be resolved, as dozens of secret files of the domestic intelligence were destroyed in late 2011.The claims over collusion between the BfV and extremists surfaced after the German public first learned about the NSU and its role in the murders in November 2011, when two members of the group reportedly died in a murder-suicide following an unsuccessful bank robbery.A third member of the NSU, Beate Zchaepe, is currently under arrest but remains silent.A key witness to the unresolved murders was found dead in her apartment in the southwestern German city of Karlsruhe last week.The 20-year-old, identified as Mellisa M., had reportedly told German lawmakers behind closed doors that she felt threatened after she had given evidence on the NSU earlier in March at a parliamentary investigation committee in the southwestern state of Baden-Wurttemberg.The NSU terror cell is believed to have been founded by three right-wing extremists who lived underground from 1998 with fake identities.Since the late 1990's, Germany's domestic intelligence agency, or BfV, recruited various informants from the right-wing scene who are believed to have had contacts with the trio.The NSU scandal shocked the German public and sparked a debate on German security and intelligence organizations which were sharply criticized for underestimating the far-right threat.