The three original 16th century texts were stolen from a cabinet in the half-timbered Luther House Museum in Eisenach, Thuringia - thought to have been Luther's home while he studied at the local school as a young monk.
Police on Monday said they still had no leads to the thieves, but were asking supervisors of two school groups who visited Luther House between 10am and 2pm on Friday to get in touch.
The stolen texts, penned by the father of Protestantism between 1520 and 1530, comprise of an address to the Christian nobility and another to regional leaders and a sermon.
The original sheets were made more valuable by the addition of handwritten notes by some of Luther's contemporaries. The theft was a “very grave loss which could not simply be replaced,” said Jochen Birkenmeier, scientific director at Luther House.
While the estimated material worth of the texts has been roughly estimated at around €60,000 they would be very difficult to sell, said Birkenmeier. “No serious trader would let themselves in for that.”
The Eisenach museum, founded in 1956 and last renovated in 1996, is much smaller than the better-known UNESCO World Heritage-listed Luther memorials in Eisleben and Wittenberg, and does not have a comparable budget for security measures such as cameras.
Even the museum cabinets are old, and police said they thought thieves had exploited weaknesses in the joints to get at the texts.
On Monday Thuringia's Culture Ministry pledged money for an on-going renovation project – and security update - to get the Eisenach museum ready for celebrations marking the 500th anniversary of the Reformation in 2017.