The North Tower definitely had its core structure shattered beforehand probably in the basement levels because the 353 ton antenna resting on the core structure fell first according to the photos and video below. However the core structure is still standing in this hi-rez photo and somehow the floors have been shattered from their connections to the core structure and are falling at near free-fall speed.

North Tower transmission tower leads collapse - - 911 Eyewitness

RDX-class cutting charges cutting through the remaining North Tower core columns - - 911 Eyewitness


Photos from a static mounted (see guy wire in lower left-hand corner) WTC1 video show the North Tower antenna which weighed 353 tons and was supported by the entire core structure fell first about 10-15 feet and fell 56 feet before the 94th floor began to fall. The large exterior sections were shattered and blown out of the building in the original What we saw - Bob and Bri video at about the 19:42 time and the core shattered which is why the antenna fell first in other WTC 1 videos. Or more likely, perhaps the core columns were also shattered in the sub-basement levels prior to the explosions blowing the large pieces out in the above video, dropping the antenna first.

Each colored segment is 50 feet