And although this is a fire scene, it is also a crime scene, which means a large unit of crime scene investigators is present, working from a tent at the corner of West St. and Liberty. (p. 194)
NYPD Detective first grade Hal Sherman: "At Ground Zero the CSU is responsible for photographing the site, recovering physical evidence...
inspecting debris that leaves the site, and inspecting debris as it gets sifted out at Staten Island. ...All evidence is documented– airplane parts were essential to the beginning investigation, but now they look for hair, fibers, glass particles, semen, ballistics. ...We ID every part. Pillars and beams are swiped for hair, tissue and blood, evaporated body evidence...
... There are two dump sites. One is in Fort Hamilton, Brooklyn, and the other is in Great Kills, Staten Island. At each location police Investigations Unit detectives and FBI agents are spotting and sifting through every truckload, searching for the flight recorders of the planes and for any remains of the victims. (p. 201)"
Law enforcement authorities survey the material for evidence. Only then is it released to a scrap processor under an existing long-term contract with the NYC Department of Sanitation to purchase and then recycle scrap metal."– Source