It emerged in Germany in November that a gang of three calling itself the National Socialist Underground was presumed to be behind the unsolved murders of 10 people, mainly shopkeepers of Turkish origin.
The Swiss national, who has not been named in line with police policy, was detained on February 7 over links to a gun that was used by the cell, which allegedly went on its race-driven killing spree between 2000 and 2007.
"The investigations began initially over the suspicion of support for a criminal organisation," said police spokesman for the Swiss canton of Bern, Michael Fichter.
But now, "mainly for procedural reasons, the charge has now been extended to complicity in murder," he added, confirming local media reports.
The German extremist cell is also believed to have mounted two bomb attacks in the western city of Cologne in 2001 and 2004, wounding a total of 23 people, and staged a series of armed bank hold-ups.
Two members of the cell were found dead in November in an apparent suicide pact and the other, a 36-year-old woman identified as Beate Zschaepe, turned herself in but has refused to speak to police.
The announcement from the Swiss police comes on the eve of a commemoration ceremony in Germany for the cell's victims which will be led by Chancellor Angela Merkel.