(Minneapolis, MN --  The investigation continues today into what caused an explosion and fire that tore through a century-old building Wednesday in the crowded Cedar-Riverside neighborhood just east of downtown Minneapolis.  At least 14 people are injured, six critically, and at least three people are reportedly unaccounted for.  Minneapolis Fire Chief John Fruetel says authorities don't know if all the residents are accounted for.  Some made it out on their own, some had to be rescued with ladders and witnesses said others jumped from second- and third-floor windows.  Fruetel says investigators have not been able to enter the building, but hope to today, if conditions are safe.  Fruetel says it could be days or weeks before a cause is determined.