Lethal blaze at Twin Towers site

Two New York firefighters have been killed and five others injured tackling a blaze at an abandoned skyscraper next to the Twin Towers site.

The former Deutsche Bank building, which was damaged in the 9/11 attacks on the World Trade Centre six years ago, was being dismantled.

Source BBC

How come this building has taken 6 years to pull down? in the report it states that one of the reasons was due to searching for 9/11 victims remains and yet on the site of the two towers the debris and very likely remains of many victims was removed to a local dump in a very short time