Investigators looking for the cause of a deadly explosion that leveled part of a Pennsylvania chocolate factory are facing an even more difficult task as they comb through wreckage that was picked apart and moved around during the weekend search for victims and survivors. Seven people were killed and several others wounded in the powerful blast at the R.M Palmer Co. plant in West Reading. With the recovery effort now over, attention turned to identifying the cause. Authorities say that task is even more complicated because heavy equipment was used to pick apart the wreckage.