The archive collapsed on March 3, 2009 killing two men in a neighbouring building and destroying scores of precious historic documents.
The city has since opened an investigation into what caused the accident and has raided the offices of construction companies involved in building a metro line underneath the building.
Now according to local daily Kölner Stadt-Anzeiger, a construction worker on the metro line has admitted that his foreman intentionally used fewer steel reinforcements at the site of the accident. The unused metal allegedly went to scrap dealers, the paper said.
The worker's statements have been substantiated by a further witness, though they were denied by the foreman, according to the paper. State prosecutors working on the case refused to comment due to the ongoing investigation.
There is also evidence that protocols for the work site may have been falsified, the paper said.
In June 2009 experts said they had recovered 85 percent of the archive's documents and were amazed by how many had survived the devastating accident.
The documents, which date back as far as 1,000 years, were in varying states when rescue workers pulled them from the archive rubble, but less than one-quarter had been torn apart. Experts have since been working to piece them back together using software that was developed to restore shredded documents from the East German secret police, the Stasi.