but, hearing no answer to her shout, melissa doi returned to the call. >> doi: can you, can you-- stayor: yes, ma'am. >> doi: i feel like i'm dying. >> pfeifer: orio palmer knew how dangerous this was, and he didn't stop. ladder 15 knew how dangerous it was. but we never thought that an entire high-rise building would collapse. there was no history of it anywhere in the world. >> pelley: but this day, history was changing, because the planes had blasted away the spray-on fireproof foam insulating the structural steel. the burning floors were sagging, slowly pulling the exterior inward. e.m.s. division chief john peruggia was in the city emergency operations center, where he received a warning from an official he believes was an engineer. >> john peruggia: he said, "the buildings are severely compromised. you can see slight lean. they're in danger of collapse." so i grabbed one of my staff guys, e.m.t. rich zarrillo. and i said, "rich, go to pete ganci-- don't talk to anyone else-- and deliver this message: the buildings are in danger of collapse." >> pelley: in this four-second video,

. >> melissa doi. >> brendan dolan. >> robert e.. >> and my father. 20 years ago today god called you home and our lives have changed since then, but the love and memory shall never pass away. there is not enough time to explain incredible man you were, you inspired me to be the parent i am, and i thank god for the years i had with you. dad, made her heart continued to beat through those who are still here, and all of the good you have done the legacy that continues to live on. god bless you all and god bless america. >> and my sister, my beloved sister diane gladstone. extended family misses you and loves you every day, your nieces miss you, your great-niece misses you and will love you forever. >> neil matthew dollard. >> james domanico. >> benilda pascua domingo. >> alberto dominguez. >> carlos dominguez. >> jerome mark patrick dominguez. >> kevin w. donnelly. >> jacqueline donovan. >> william h. donovan. >> stephen scott dorf. >> thomas dowd. >> kevin christopher dowdell. >> mary yolanda dowling. >> raymond matthew downey, sr. >