Someone (I forget who) on CNN made the point that the only thing missing from her apartment was her keys. She had left her purse and cellphone behind. The person on CNN asked where would you be going if you only took your keys? To visit someone who lives in the same building. The person speculated that if she had been going outside the building, perhaps to run a quick errand, she most likely would have taken at least her purse and probably her cell phone too.
The police need to find a body or some other evidence of foul play so they can change her status from missing person to homicide victim before they can start naming "suspects".