The detective, identified only as Ellen H., revealed the planned assassination during the trial of Beate Zschape, suspected of being the last plotter still alive, The Local.de reported Wednesday.
The Munich court was shown a 2002 photo collage in which then-Chancellor Gerhard Schroder was depicted behind bars with a Star of Davis on his chest. Underneath, written in English, were the words "You are the next one."
The detective said she found the collage during a search of a hard drive found in the ruins of the group's apartment. They were members of the neo-Nazi National Socialist Underground.
Zschape is believed to have set the residence on fire after two other members of the group committed suicide.