I like the "she was murdered" theory....for everyone who says why didn't they just throw her off the roof? That would have drawn attention. That would have got the killer(s) caught. Leaving her in the water tank not only gave them two weeks before anyone found her, but by the time they did find her she was so badly decomposed that they couldn't properly test for drugs. If someone killed her they did it brilliantly.

Though the was probably just crazy.
Nah if someone is chasing you, you wouldn't be pushing buttons, waiting for the elevator to close, and making weird hand movements. You would haul ass down the stairs to the lobby and call police.