I disagree on the "type" theory. I think the perp prefers small, petite women with long, dark hair. The Taiwanese woman was petite, as was Brianna. Both were small, around 100 lbs. IIRC.
This would make sense considering he took the Taiwanese victim from behind. He probably did the same to Brianna. He probably prefers smaller women because they're easier to control and probably has a preference for women with long dark hair. He could also be going after long haired women because he can use the hair to his advantage (by pulling/grabbing it) to control them further.
BTW, if the plate at the base of the doorknob has screws on it, he could remove the screws on the plate to facilitate easy removal of the doorknob.
I think he picks petite woman for the simple fact that he can overpower them easier than a large frame woman. Most asian women are petite. He would have more control over them. I was tickled to death that the one victim kicked him in the head & fought back!