(Oregon City, OR)  --  The preliminary investigation into the arson at the former Blue Heron Paper Mill in Oregon City is complete.  Officials say the building was badly damaged in Saturday's fire, and that's making it difficult for investigators to safely get inside.  Clackamas Fire investigators are coordinating with the Confederated Tribes of Grand Ronde to safely continue the investigation and remove the fire debris.  A suspect was taken into custody the day of the fire.