What does the ending scene in the movie Basic Instinct actually mean?

The answer is much more complex. There are two fully developed storylines throughout the whole film. In one storyline, Catherine is the killer. In the second storyline, Beth is the killer. If you look back at the story very carefully both in the movie and the screenplay each is presented. The ending concludes both storylines. The Beth as killer concludes with the first fadeout. The second fadeout is actually an alternate ending. The ending in which Catherine is the killer. It's kind of a choose your own adventure. That's why you find almost as many people viewing Catherine as innocent, (maybe that could hardly be the word) but at least not the killer, as those who believe her to be the killer. Each viewer has made this decision as to which storyline to go with, to believe, based on their own personal predilections. Look at it again. All the clues are there for BOTH story lines. Can you see them? Or do your personal prejudices get in the way?

The last scene is to clear up who the killer is.

In the end Catherine Tramell tries to pick up the ice pick in the sex scene which is her murder tool from the first kill, which signifies that she was the killer from the start. The killer was never caught, but after the death of Beth and the evidence found at her house, it turned out that she is the killer. But she was all innocent, and it's been all Catherine's revenge plan because Beth was her lesbian partner and left her.

My answer is based on the truthfulness of following premises, as shown in the movie:

1. Dr. Garner (Lisa Hoberman) has been depicted as being obsessed with Catherine.
2. Catherine is a brilliant psychologist, who is writing a book (thought to be an alibi), the chapters of which depict the murders happened.

I think, there is not just one killer. Dr. Garner, Catherine, Hazel Dobkins, Roxy- All have murdered. The thing is Beth, Dobkins and Roxy are highly obsessed with Catherine. She makes them murder all the people except in the first scene (where she herself murders Johnny Boz). She is a brilliant psychologist who reads the characters really well. She knew that she could make em do anything she wants.

• What's the deal with writing a book?

  Well, Catherine is a writer and a psychologist, it makes sense for her to write a thriller? Not exactly, the book is the live proof that she wants the police to think that the book is an alibi (that's why she talks about it being an alibi in the interrogation scene-You know, shape their thought to course a direction she wants. She knows how human mind works really well), and she also puts up an open kinda challenge that, she will make all the murders happen and describe them in the book but no one can prove that(or make em wanting not to prove, or ignore it, after manipulating their state of mind).

• Okay...but the books were found in Dr. Beth's drawer and all the straightforward evidence points her to be "the" killer of the movie?

  Again nicely played by Catherine. Beth didn't kill Gus, it was Dobkins, who killed Gus with such cruelty. Beth didn't have anything against Gus. Beth just happened to be there coincidentally. The evidence, was planted- Remember when Beth tells Nick to take the cigarettes from the top Drawer- the books were found later in the top drawer- if Beth was the ultimate verdict, why would she risk herself?

• Catherine didn't dispose off Nick to the end- Why?

  She would have, but at each point Nick turns out to be the unexpected character when she thinks she has captured the character of Nick, she finds his new side. She just can't kill him until she finds everything about him- like "the F**k of the century", his challenging character who is not scared of her and wants to the play the "game" even if it means his own death, his above average intelligence and extraordinary observation power etc. So she tests Nick's level from the beginning and the night she tells him that the book is finished and the Detective dies, she killed the detective character in the book because she found out that Nick believes that Beth was the mastermind and so he couldn't find the actual killer, now the actual killer is going to kill him- which is herself.

  She then says good bye to Nick and she cries (for real) because she knew she was going to have sex with him one last time and then have to kill him. Nick on the other hand completely believed her innocence and actually "fell for the wrong woman" but guess what- at last she also fell for him (this is what she never anticipated actually- thought she could be a master of all the puppets). Anyway, the last time she picks up the ice pick to kill Nick, she just couldn't as she was already in love with him. She decided to spare him and, fu*k like minks forever.

When Nick visits Catherine Tremell he reads a page as it's being printed from her book. It describes his partner's death (Gus) while he (Nick) is running up the stairs to save him. This was written before Gus dies hence Catherine is the killer. Nick realises this while waiting in his car and hence the dash to room 405. No reason then for him to kill Beth.

...one thing that everyone missed here is that Beth said that her door didn't lock properly.

So, Catherine could have snuck in to her place, planted all the evidence and then set Beth up by sending her to the fake address. Catherine was pinning everything on to Beth to gain revenge on her for what had happened in high school.

She could have easily set up all the materials required as she was a writer.

Which ever way you look at it, Douglas was 50 when he did this. Far too old for both of them even at the time ;D

You're all missing the point; Beth had to be innocent because she had not read Catherine's latest book and did not know the detective's partner gets murdered in a lift on the fourth floor. Only Catherine knew that so she HAD to be the killer.

Is there any chance that both Catherine and Beth are the killers? They've been in love ever since they studied together and they are both very sick-minded, both of them plan all of the books and murders, let's say "just for fun", until everything gets out of control and Beth ends up getting killed.

Or even better, Catherine being one step crazier (since she has been a murderer longer, starting with her own parents) wants a different ending to the book they had planned and twists the story to the point of killing her partner?

To me these theories make a lot of sense since otherwise, how do you explain Detective Nick being involved in the whole plot from the very begining of the movie and even before that (being in a relationship with Beth). There is no way that everything that happens surrounding Beth is mere coincidence or planned perfectly accurately by Catherine alone.

AND one more detail, even if all of the evidence was planted in Beth's apartment, there is one piece which doesn't fit: she says she supposedly arrived at the building because Gus had left her a message and when the police checks afterwards, they say there is no message in her machine; there is no chance that Catherine or anyone else could have erased that message, unless they had both been the murderers all along since the beginning.

If Beth is not the killer, then she must have seen the murder. She was on the floor. Or, If she came up the stairway just after the murder she would have passed the killer and the bloody clothes. But she mentions none of this.

If she is not the killer She would have parked outside the building. Nic would have recognized her car. So, it must have been hidden.

A report was made to berkely security about Beth. We don't know what it said, but Nielson had it and it is missing.

Catherine could be the murderer, but that requires an elaborate frame. Yes, for Beth to be the killer does require an amazing coincidence. I find that coincidence _- the manner of Gus' death to be more likely than the elaborate planning required to set her up going back to their freshman year.

Catherine killed every one and drove the dr crazy and got him hospitalized so she could add another chapter to her book. He was her muse, that's why she paid him respect and brought him a copy of her book. Whatever he was, he was in the psych ward because he was the main character... That's why he smiled in the end ...of joy. But the real pain he's in there for killing the officer which is the only one who knew the real truth. HE WAS INNOCENT AND CATHERINE WAS THE THRILLER KILLER.