Because EL was, for some reason, visibly impaired, she couldn't remember which floor was hers, so she went to the 14th floor, because she remembered it was a middle button, and perhaps confusing the floors "4" with "14". She tried to enter what she thought was her room, and this alerted the occupant of that room.
She comes back to the elevator.
Elisa Lam Video - YouTube
Start the video.
0:07, she's trying to read the numbers, but can't, so she just hits all the buttons in the middle row, and then hits the "HOLD DOOR" button, thinking it reads, "CLOSE DOOR".
00:20, the occupant has left the apartment, is holding the elevator button in the hall, and is outside the vision of the camera. He says calmly, "hey, get out of the elevator."
00:24, she checks the hallway, and sees the man standing by the button. She positions herself to view the the man, and is waiting for the elevator doors to shut. The occupant holds the button to the elevator, and calmly asks who she is.
00:37, She approaches the man and attempts to apologize.
00:48, the occupant tells her to get out of the elevator. She shyly and slowly begins to, but sees danger.
00:53, the occupant pulls out a gun, and this causes her to jump. The occupant says, "spread your legs", and she complies. The occupant is now telling her to come closer to him. She doesn't understand there's a camera in the elevator, while the occupant is fully aware of this.
1:03, the occupant grabs her at gunpoint, makes her place her hands on her head, demands to know who she is and what she's doing there, and tells her to get out of here or he'll kill her, and he says, "you've got 20-seconds to get out of here". and he releases her.
1:30, she enters the elevator and is terrified. In a panic, she hits all the buttons in the middle row, but she keeps hitting the "HOLD DOOR" button. The man is counting down, and she doesn't understand why she can't leave.
1:50, exactly 20-seconds later, the occupant hits the button again and orders her to come back. She's in tears and is trying to say she's confused. The occupant doesn't believe her.
1:57, the occupant grabs her neck and places his gun on the back of her head, she's pulling away, giving the strange look about her arms, because she's trying to trigger the sensor to keep the door open.
2:05, the occupant notices what she's doing, grabs her neck, and gives her a yank and tells her to shut up, and she completely submits.
2:12, she begins begging for her life.
2:20, the occupant orders her to be quiet.
2:25, the occupant leads her away from the camera by her neck, and a gun to her head.
2:45 (aporox) the occupant lets go of the elevator button.
2:58, the elevator shuts, and begins going to the floors pressed.
It is my belief she was accosted by an occupant of the 14th floor, probably someone in a room with a fire escape access to the roof. My belief she's on the 14th floor is because of this picture...
http://i.imgur.com/we6I2JX.jpg
...this is a picture of the buttons in the elevator in that video. According to this, she kept hitting all the buttons in the middle row, in this order from top down, 14, 10, 7, 4, M, B, and "HOLD DOOR". She was staying on the 4th floor, and I believe made a simple error, due to not wearing her glasses, where she picked "14".
You'll notice in the video that the top button in the middle row does not light when she presses it. That is because, as you see in the photo, it's the button for the 14th floor, and she's already there.
What happens then till she ended up in the tank is anyone's guess, but I believe her time was very quick. Check out this news report from Stephan Chase for KTLA News, specifically the testimony of Bernard Diaz starting about 1:30 in. He talks about an "explosion" that "knocked him out of bed".
http://www.google.com/url?sa=t&rct=...zOe-qfczXuQhyUg&bvm=bv.42965579,d.b2I&cad=rja
This "explosion" was caused by Elisa taking off her clothes to better swim, and the clothes clogging the pipes. This caused a separation of water in the pipes, which causes a vacuum effect that will eventually fall to it's own pressure and "burp", typically resulting in a very loud noise and pipe damage. I do believe flooding was reported about that time.
It is my belief the occupant took her almost immediately to the roof, and ordered her into the tank, sealed her in, and simply went back to his room. The motive being that he's a paranoid schizophrenic and he viewed her as a threat, because she made the mistake of going to the wrong floor, and she tried to enter the wrong room. Based upon this, it would be a person suffering from this illness that also occupies the 14th floor.
I believe EL died of hypothermia within hours. The cold fresh water slowed her decay process, but in the middle of the month the temperature rose to 60, causing her body to decay, giving the blackish tint and the belief then was when she was placed in the tank.