Kind of a plot hole (SPOILER)
How does Klute get into the dress factory at the climax, when the place is closed for the night?
I presume the killer was trailing Bree, and watched what floor the elevator went to, then followed her and hid among the mannequins. (Which, okay, is a bit of a stretch, but doable if a criminal puts their mind to it.) (At least the place is unlocked at that point.)
But then the employees we've seen leave, and for some reason they think it's fine to let a stranger stay behind to use the phone while they're on their way out.
So, are we to presume that they left the door unlocked for Bree to let herself out? How else would Klute get in to save her? WHY WOULD ANY BUSINESS, ESPECIALLY IN NYC, DO THIS???