Police last October reported that genetic material found near the skeleton of nine-year-old schoolgirl Peggy Knobloch, who went missing in 2001, matched that of the late neo-Nazi gunman Uwe Boehnhardt.

This seemed to connect the child's death to the 2000-2007 racist murder spree on the National Socialist Underground, far-right militants who shot dead nine men with migrant roots and a policewoman.

But it has now been established that the DNA found near the girl's corpse was in fact inadvertently transferred there through “police equipment” from Boehnhardt's corpse, said prosecutor Daniel Goetz.

Boehnhardt and his accomplice Uwe Mundlos had died five years ago in an apparent murder-suicide following a botched bank robbery.

It remained unclear which piece of police equipment had been used in both cases, Goetz said, but media reports have pointed at a measuring stick police use on crime scenes.

Something like that “should not have happened,” admitted Uwe Ebner, who leads a special inquiry into the child murder.

Knobloch vanished on her way home from school in 2001 near her home, in a high-profile case that captivated the nation.

Hundreds of police and soldiers scoured the area for weeks, but her remains were only found in July last year, some 15 kilometres (nine miles) from her home, by a mushroom picker.

After her death, a man with a learning disability spent more than 10 years in jail for her murder before he was exonerated and released, as police resumed the search for her murderer.