More than 7,000 irreplaceable documents -- including historic decrees signed by Peter the Great -- have been stolen from St Petersburg's state archives.
Thieves helped themselves to handfuls of ancient manuscripts from binders in bundles of up to 50 before making their escape from Russia's biggest historical archive, on Millionaya Ulitsa.
St Petersburg man Anatoly Feinberg was arrested in connection with the theft last Friday.
Police believe Feinberg, who spent three years in prison after being convicted of stealing documents from the archives' reading room in 1984, bribed a security guard to give him a "free run" of the venue.
Detectives visited Feinberg's apartment soon after the theft was discovered. They said some 300 of the stolen papers were discovered there.
Individual letters with immeasurable historical value are stored at the archive which has 86 kilometer-long shelves as well as statutes from the imperial Senate which can run to 1,000 pages.
Director Vladimir Lapin said, "It will be very difficult to establish the value of papers that have gone missing. The oldest ones here date back to the 13th century.
"We know some decrees signed by St Petersburg's founder have been stolen. They are of immense historical importance but it is impossible to say how much the would be worth in cash terms."
Mr Lapin went on to say that all the stolen documents were kept in depositories in unsatisfactory conditions. Only 3% of material is stored on microfilm.
Bosses had constantly lobbied the authorities for cash to renovate the archives.
But the Russian State Archive Service had failed to tackle the problem.
The building had once received money -- for a fire safety system in 1993 -- but the funds soon ran out and the project was never finished.
Mr Lapin believes the full amount of stolen documents has yet to be established. A search is continuing to check what exactly has gone missing.
As soon as last week's theft came to light curators began to find plundered binders in different places around the archives making it difficult to assess the full extent of the damage.
Meanwhile a senior employee at the Russian Museum has been charged with the theft of eight drawings by Russian artist Pavel Filonov from the museum collection.
He was charged last week by agents from the Federal Security Service and has been fired from the museum.
Police have not named the suspect but the arrest follows a widescale investigation which revealed a large part of the Filonov collection could be fakes.
Detectives believe that a sophisticated gang of art thieves stole paintings to order before replacing the originals with cunning forgeries.
The KGB began investigating the case five years ago when they discovered eight Filonov works in the Museum of Modern Art in the Georges Pompidou Center in Paris.
Museum director Vladimir Gusev said the copies were "professional" and it was almost impossible to tell them apart from the originals.
Filonov's sister Yevdokia Glebova removed her brother's works from the collection seven times and detectives believe this is when the thieves could have struck.
The investigation continues.