German domestic intelligence agency reportedly ignored for years an important CD containing clues on the existence of a neo-Nazi cell known as the National Socialist Underground.

German weekly magazine Der Spiegel reported on Thursday that Dr. Hans-Georg Maassen, Director of Germany's domestic intelligence agency BfV, told senior lawmakers of the interior committee that agents had this week found a CD in an archive labeled "NSU/NSDAP" which had been sent to the agency in 2005 by a far-right informant.

His remarks contradicted earlier statements by BfV officials who repeatedly claimed the agency heard about the existence of the National Socialist Underground group (NSU) only in 2011, when members of it were identified by police after an unsuccessful robbery.

The neo-Nazi group killed eight small-business owners of Turkish origin, a Greek immigrant and a German policewoman between 2000 and 2007, apparently without arousing the suspicion of the police or intelligence.

Two of the murders were committed in 2005 - the year an informant sent the CD to the domestic agency.

The group killed two Turkish immigrants in 2006, and a German policewoman in 2007.

The German public only learned about the NSU and its role in the 10 murders in November 2011, when two members of the organization reportedly died in a murder-suicide following the unsuccessful bank robbery.

- Questions unanswered

Until 2011, the police and domestic intelligence services excluded any racial motives behind the murders, instead treating as suspects immigrant families, mafia groups and drug traffickers.

The third alleged member of the group, Beate Zchaepe - currently held under arrest as the main suspect in the case - has refused to give testimony in her trial, with her lawyers saying she will remain silent throughout it.

Many questions related to the NSU's murders have yet to be answered, as dozens of secret domestic intelligence service files were destroyed in late 2011.

Clemens Binninger, President of the Federal Parliament's Parliamentary Control Panel (PKGr) which oversees the activities of Germany's intelligence services, called for a special meeting on Monday to discuss the details of recent revelations about the CD.

Green Party lawmaker Hans Christian Stroebele, a senior member of the PKGr, criticized the German government for not displaying determination to solve the NSU murders.

"Both the domestic intelligence agency and the federal government have failed to shed light on the NSU scandal," he told Der Spiegel.