 An investigation by NIST concluded that the collapse was caused by a combination of damage to support columns and fire insulation from the aircraft impacts and the weakening of columns and floors by jet fuel ignited fires.NIST also found "no corroborating evidence for alternative hypotheses suggesting that the WTC towers were brought down by controlled demolition using explosives planted prior to September 11, 2001".Jones, among others, points to many descriptions by individuals working on the WTC rubble pile suggesting the presence of molten steel in the pile and a stream of molten metal that poured out of the South Tower before it collapsed as evidence of temperatures beyond those produced by the fire.