WHy did his trousers ripped? See picture.
I also guess that he might hit the ground shoulder first, which might indicate that he might be alive until he hit the ground.
As for the ripped trousers, I believe that someone, or some people might be holding on to his legs and trousers out of the windows before he fall. Alas, the strength of this person or people (if more than one) is not enough to hold on to him.
This person's (or people's) intention could be just scaring Teoh, eg by threatening to let him go from their grip, but Teoh might have struggled and they couldnt hold on to him, so Teoh fall to his death.
Well thats just my theory, you might have one better.