Investigators are going to question a homeless man about the Greenpoint Warehouse Fire from last May, according to WNBC. The hypothesis seems to be that the man, along with other homeless men, "might have been attempting to burn the insulation off the copper, which may have been what caused the massive fire." Both the FDNY and Bureau of Alcohol, Tobacco, Firearms and Explosives have investigators involved. But arson is still another possibility.
Update: Police have officially arrested Kuczera Leszek on arson, burglary and other charges.
Photograph from Michael G. Chan at daily snapshots, who also has pictures of the fire in its second day
