Effective Definition of Freefall (in the case of World Trade Center 1)

You can see the object emerging from the dust on the right, just above the ejection.

This object is a corner section. The red outline marks the speed of the collapse front along the SW edge of the building.

The next two photos show that this object lead all others in the fall by quite a wide margin.

You can see the falling piece just above the light pole on the right.

Here you can see the falling piece along the SW corner (the right-most corner) even with the top of a building. Please look carefully along the top of the building just above the trees.

It leads all other objects in the fall by at least 14 stories.

This angle also shows us that the object is falling near to the SW corner. It is a corner segment, so it is probably from the SW corner collapse initiation zone.

It is clearly the definition of freefall, more so than any other object.

The falling object is visible in both images below.