Hi, I'm a newbie here (I found this site when someone on a different forum where they were briefly discussing the elisa lam case linked to it). I've been reading the pages and pages of posts and have some thoughts on it.
First, I think this definitely wasn't suicide as some people were suggesting.
-Elisa had plans to continue onto Santa Cruz. She seemed like she was looking forward to the rest of her trip.
-She was keeping in contact with friends and family and didn't seem like she was extremely depressed at this point in the trip
-Physically I think it was impossible. How would she have closed the lid of the tank after entering it? She would have had to had superhuman strength to grip the edge of the tank opening with one arm while reaching up towards the lid with the other arm. Most people, especially girls don't have that kind of upper body strength in most cases (I'm about her proportions and definitely wouldn't be able to do that). And this is assuming the tank was full of enough water to be able to float near the surface and suspend yourself near the opening. If it was only 1/2 or 3/4 full I don't see how she would be able to reach up to the opening hatch. However this is assuming that the tank lid was actually closed when the maintenance guy found her.
-In addition, where are her clothes? She would have been having to walk naked around the hotel or have thrown her clothes off of the roof. But if she is modest like her friend that posted earlier about her shoes said, I don't think she would have gone naked into a water tank.
-A water tank is definitely not what I would call an inviting place to die. If it was night time she probably wouldn't have even been able to see anything inside (it would look like a pitch lack hole). Why would you drop into a pitch black huge empty space, naked? Wouldn't the thought of being in a black hole with no way out feel claustrophobic?
-I also don't think it is a suicide due to the manner of the death. If you look historically like in medieval times, one of the worst crimes a person could commit was poisoning the town well/water supply. To kill yourself in a water tank means you're knowingly contaminating the water for all the residents of the hotel. This would be an act of anger/aggression/hostility towards the residents of the hotel/people in general. Even though Elisa wrote about being depressed, I never sensed any particularly excessive bitterness/resentment towards others. She seemed introspective not like the type to lash out. I also think, given her penchant for writing, she would've left some sort of note.
I think Elisa was murdered (or deliberately left to die).
This is what I think happened. In the elevator video, it seemed like she was playfully interacting with someone, possibly playing hide and seek (That's why she was poking her head out and jumping back in to hide, and also why she was pushing multiple buttons to hide her location). I think she was playing with someone who was around her age and seemed trustworthy, either a friend she recently made at the hotel (could have been a hotel worker she made friends with), a friend from an online meetup, or a friend of a friend.
Somehow they ended up hanging out on the roof. Probably just to keep hanging out, take photos, look at the stars, drink, I don't know. But I don't think she was forced onto the roof. She could've screamed for her life but she didn't (unless she did but people just ignored her) if she was being forced. I just know if I was being forced onto the roof I would assume the worst and try to get the help of the people on the hall rather than go to the secondary location with a threatening person. I don't think she was too incapacitated at this point because she had to have been able to climb the fire escape herself. She might have been under the influence of some drug though that she took either willingly, or unknowingly (I think she was probably slipped something).
Once they were on the roof, after some time, she succumbed to the drug and went unconscious. She may/may not have been sexually assaulted but she probably was since she was naked. Her assailant carried her and dropped her into the water and closed her into it. She may have woken up in the water or she may have immediately drowned or she may have already been dead. But even if she was alive she would've died within a few hours due to the cold water and her weakened state (at her body weight she probably had very little fat to help keep her warm).
To address some points people have made:
-I don't think she would've been hard to carry. I read somewhere here she was about 5'4" and 115 lbs. I'm about the same size. My boyfriend can easily walk around with me in his arms or on his back and he's just an average sized guy. The assailants adrenaline rush would have made him even stronger (you read in the news about mother's lifting cars when their baby is trapped under and stuff like that). Fear/panic can give people superhuman strength. So I don't think she had to have been the one to climb up the water tank.
-Diaz's claims that he heard a loud bang that night: I think he was either making this up (people can either do this deliberately or unintentionally have a false memory), or he actually did hear a noise and that was Elisa's body hitting the water or possibly her thrashing around inside if she woke up. Or it could have been the suctioning at the bottom that another poster mentione earlier.
-People have been talking a lot about her not wearing glasses. I don't think this is very significant. She might've been wearing contacts, or her vision might not have been so bad that she couldn't function normally without them. For example, if it was night time and she was just going to the toilet she might not have bothered putting them on.
-I do not think she was on her way to the shower. Her shoes didnt look like what a girl would wear in the shower (probably would wear flip flops) and she had no shampoo/wash cloth/towel/brush/change of clothes that a girl would normally take with her.
Who the killer was:
Like I said before, I think this was someone she trusted. I think she followed them onto the roof willingly (although her decision making skills were probably influenced by the drug). Still, to accept a drink/food/pill from a person, she had to trust them to some extent.
I think that it was someone she met at the hotel and quickly bonded with (or someone associated with that person who she trusted by association) or a friend she met online and was supposed to meet in LA. For her to feel comfortable with the person, they are probably in her age group and pretty normal seeming.
Also, I think they are pretty smart because they were able to think to put her in the water tank (hidden from view, destroys evidence, unlikely to be discovered). If it was some junkie from skid row I think they would've left her body out on the roof top or thrown her off the roof in a panic. This person is probably fairly strong to be able to carry her up the water tank. Since this person is familiar enough with the hotel to know the layout this well and how to get onto the roof and confident not to be discovered, I am strongly leaning towards that it is someone either staying there for a prolonged period of time (by this I mean someone who'd been there at least a week or even a log term resident) or a worker at the hotel who she came to trust.