On the Acquisition of Mosquensis

The codex Mosquensis is a famous book that was found in 1777 by Christian Friedrich Matthaei in the library of the Synod in Moscow, and which includes part of Homer, and also the Homeric Hymns. It's famous because it contains our only copies of the hymns to Dionysus and Demeter, while all other manuscripts of the hymns open with the one to Apollo. In his edition of the Hymn to Demeter Richardson states simply that Matthaei "discovered" it, while Allen, in his edition to the hymns, says that he "acquired" it. But recently I read the History of Classical Scholarship by Wilamowitz, where he writes quite bluntly that the manuscript was "stolen" (gestohlen) without going into more detail. I'm curious about what actually happened. We know that he sold it to Ruhnken, the hymn's first editor. But I appreciate such details, and since I've mentioned this discovery before, I thought I would pass it on.