The second site is not far from the one currently being searched.
The German site has become a main area of focus for the investigation.
"We'll draw a line at some point."
The searches are taking place 20 minute's drive from the area Madeleine went missing in.
She went missing in 2007 while on holiday with her family.
The first letter said they were treating Madeleine's disappearance as murder after uncovering new evidence.
"Countless children's items, most of them small swimsuits."
Prosecutor Hans Christian Wolters has speculated she's no longer alive.
He said his earlier claims that Madeleine is dead were his own private opinion.