He is in prison for raping an elderly woman.
"We are pleased with the response to our appeal for witnesses."
The revelations come days after her parents marked what would have been her 18th birthday.
The German prosecutor leading the case says he may be charged "in the next three months".
He said if the public knew what evidence authorities had, they would "come to the same conclusion as I do".
"There are leads, tips and lines of enquiry from those witnesses that urgently needed to be followed up."
A whistleblower said "very serious crimes" had occurred at the property.
The incident occurred ahead of his parole hearing on Monday.
The second site is not far from the one currently being searched.