After reviewing this case thoroughly and watching the Netflix series as well I can say I've come to the following conclusions:
The lid on the tank: LA does not experience a true Winter like a lot of the states. The average temperatures around that time period she died would have been around 50-70 degrees. Therefore it would make sense that there would be a strong presence of flies around that tank and inside of it if the lid was open. I don't remember this being listed anywhere in the investigation or on the series. It is possible this was the case and it wasn't mentioned, but that would be a decisive indicator that the lid was in fact open post death. The fact that it isn't mentioned leads me to conclude the lid was closed post death and upon discovery.
This being said, I firmly believe Elisa could have opened this lid herself and have it close behind her all on her own. The lid was most likely made of tin/steel and was only about 16"x16". If the lid was only opened part-way for entry, it could very easily slam back down closed. This conclusion would also indicate that entry was not accidental. Many people speculated that she fell into the tank from the above structure next to the tanks. I do not believe that to be the case here. I believe the lid was closed prior to her entering the tank as well as after.
The elevator tape: There is a lot of mystery surrounding this tape. However many things have been resolved. It can be concluded that Elisa did press the 'hold door' button in the elevator, causing the door to hold open for close to two minutes. Therefore there was nothing wrong with the elevator. It was functioning normally. The tape is slowed down, and not the full tape has been released. I do not believe this to be malicious intent and the video was most likely slowed down in spots so that Elisa gets more screen time-in an attempt to help those identify her and jog their memories. Many people also claim that a second person's foot is visible at a certain point in the footage. I also believe this to be not true. I believe that foot belongs to Elisa and would be consistent with her movements and placement of that foot.
So then the true mysterious part in my opinion - why did Elisa press so many buttons? Why was she on the 14th floor? Why did she only press buttons in the middle column of buttons?
The middle column of buttons contains "14, 10, 7, 4, M, and B" followed by the "door hold" button. In this hotel, M stands for Mezzanine and B stands for Basement. Elisa stayed on the 5th floor during her entire stay at the Cecil, so why would she only press the buttons in this column? The fifth floor's button was located in the last or third column of buttons. This leads me to conclude that either 1. She wasn't trying to go back to her room, 2. She was not in a functioning mental state and could not decipher how to operate the elevator, or 3. She was attempting to 'stall' the elevator or be deceptive in some way. She hung out at the elevator for a couple of minutes, therefore number 3 doesn't seem like a viable option. Elisa stayed on floor 5, she was on floor 14. Her behavior indicates to me that she is either in a poor mental state or that she is paranoid. This could indicate she was doing something she knew she shouldn't be. The fact that she ended up on floor 14 indicates that she was attempting to go "up" from her room. There is no other known footage of her in the elevator system so it is possible she used the stairs to get to floor 14 and was attempting to go back down. Why she would do that is also unknown. Only one of the stairwells in the hotel had roof access, the one she headed towards after exiting the elevator a final time. It is also worth noting there is a 15th floor button on the elevator. This indicates that with a key, the elevator could access the roof as well. On the roof, There is a set of double doors that exits below where the stairwell access comes out. This I believe is the access door that leads to the elevator. I have not seen this mentioned anywhere but this could open up more possibilities. If foul play was indeed present, if someone had an elevator key, they could theoretically move her body to the roof using the elevator and avoiding the access ladders from the fire escapes. However, this would also have been caught on camera then. So either the hotel did a massive cover up (unlikely), or this simply didn't happen.
I do believe Elisa was searching for a way to access the roof. It is a possibility she climbed the stairs all the way to the access door and realized she may have set off an alarm. The door was alarmed and set off an alarm at the main desk of the hotel. Note this was not audible from the 14th floor. However, Elisa still could have panicked and thought that if someone was coming they would use the elevators. So in an attempt to 'stall' the elevator, she pressed multiple buttons which would delay how quickly the elevator got to the main floor. This theory is flawed though since there is multiple elevators. It is worth noting this could be why she appeared to be "hiding" and searching for someone outside the elevator. It is also possible that she was trying to gain access to the other elevator on that floor in order to also stall it. I could not conclude why she would only press buttons in the middle column vs all of the columns. After this in an additional effort to elude, she decided to go out onto the fire escape and head to the roof anyway. She then chose to hide in the tank she was found in. This theory is somewhat far-fetched but i do believe it is possible. I firmly believe she was attempting to elude something. Whether that be hotel staff, another guest, or someone else. Her behavior either indicates mania, or paranoia. She definitely appeared to be fleeing someone. It is possible however that it was someone only she could see.
Edit - Upon further reading I am unsure if the rooftop loft/attic can be accessed via the inside of the elevators. Another discovery is that the door at the top of the staircase inside the hotel can only be opened from the inside. It is known that Elisa did not have a phone on her when found so it is possible she became trapped on the roof. She might have explored every option to get back down and was too afraid to use the fire escape ladders. She eventually got to the water tanks and possibly thought they were an option back down, it was dark, and with no light source it is possible she didn't notice they were filled with water.
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