What evidence exists to support the claim that molten steel was present at the World Trade Center site following the 9/11 attacks?

Multiple eyewitness accounts and video footage from the World Trade Center site following the 9/11 attacks show molten steel flowing and glowing, indicating high temperatures. Additionally, analysis of debris samples revealed the presence of molten steel and iron-rich microspheres, suggesting that steel had melted during the collapse of the towers.