You should look into Engineers for WTC. Each floor as it would hypothetically fall down will incur resistance as it hits the floor below it. Even if all floors pancake, the resistance will slow down the descent drastically, so it couldn't be anywhere close to freefall speed. Also that partial collapse you linked is drastically spread outside its footprint. That isn't the case for the WTC7. As for the pre planted demolition charges won't work. Severe Structural Compromise needs to happen ALONG with shape charges. A controlled demolition requires enormous work to cut steel members almost all the way through, on each floor, and to remove the concrete cladding that covers them.