A 63-year-old former officer who already has a police record over previous far-right crimes and his wife, 55, were detained on Friday in the Bavarian town Landshut in the case that has sparked a row over right-wing extremism within German law enforcement.

“Both are suspected of sending several emails with insulting, hate inciting, threatening content to parliamentarians and various other addressees,” said Frankfurt prosecutors in a statement.

READ ALSO: Hesse police face claims of links with far-right scene

The unnamed suspects have since been released as prosecutors said they did not have sufficient evidence as yet to remand them in custody.

But investigators were combing through data carriers seized from the suspects.

The anonymous messages were all signed “NSU 2.0”, a reference to the German neo-Nazi cell National Socialist Underground that committed a string of racist murders in the 2000s.

The so-called “NSU 2.0” affair has already claimed the scalp of police chief Udo Münch of the state of Hesse, who resigned after it emerged that police computers were used in the search for details about a far-left politician who subsequently received one of the threatening letters.

Germany's defence minister last month ordered the partial dissolution of the elite KSK commando force over right-wing extremism.

While right-wing extremism was once thought to plague mostly eastern states, Hesse was shaken last year by the murder of pro-migrant politician Walter Luebcke, allegedly at the hands of a neo-Nazi.

It was also in the Hessian city of Hanau that a man gunned down nine people of foreign origin in February this year.

READ ALSO: What is Germany doing to combat the far-right after Hanau attacks?