The German newspaperthe Kölner Stadt-Anzeiger reported Monday that the tragedy was likely caused by ground water seepage at the construction site. "Everything points to a problem with the ground water," a source told the paper. City prosecutors have now appointed several experts to determine exactly what happened at the underground railway construction site. They are trying to determine whether water seeped in through the more than one-meter thick concrete side wall or came up through the floor, which hadn't been finished. They are also looking into whether the problems might be related to rising levels of the Rhine River, which is located very close to the archive.
Meanwhile, Christian Hillen reports that a cabinet containing medieval seals was recovered today by firemen, and the seals are undamaged. For those able and interested in volunteering to assist in the recovery effort, they can contact Claudia Tiggemann-Klein (caludia.tiggemann-klein[at]stadt-koeln.de). If you are interested in making a donation, please see either
http://www.archive.nrw.de/Kommunalarchive/KommunalarchiveI-L/K/Koeln/index.html
or
http://www.stadt-koeln.de/5/kulturstadt/historisches-archiv/