Police gave no details of how the allotment search is connected to the case or what they hope to find.
Police in Germany arrested a suspect accused of stealing officer's weapons on Friday, after a five day manhunt in the Black Forest for a man nicknamed "Rambo".
A documentary is being made which follows their fight.
The German Chancellor, Angela Merkel, met with Italian premier Guiseppe Conte Monday, ahead of the EU summit on Friday, but said that the positions of the member states remain apart. But she urged her counterparts to consider the bigger picture.
The 36-year-old was able to reproduce an entire set of famous landmarks, including the Leaning Tower of Pisa and the Eiffel Tower, on his field in northern Germany as the country took over the EU Council presidency.
From post-Brexit trade deal negotiations to agreeing a coronavirus recovery fund, Germany's EU presidency inbox is already filling up.
The investigation was launched in October after police arrested a man in Bergisch Gladbach, near the western city of Cologne.
Macron and German chancellor Angela Merkel held talks on Monday before the negotiations continue at the next European council.