What I think the end meant (SPOILERS)

I am not at all sure I understood the ending, or who did what. So before I read other posts to see what others say, here's what I thought.

When I saw the DVD the first time, I thought the end meant that Susan (the long-haired woman) had done the killings, or at least some of them. And had killed her father five years earlier. But I was confused, because I also thought Sarah had killed, as well. And I wasn't sure what the picture of the guys with the two women meant.

When I saw it the 2nd time, I decided that Susan and Sarah had been in cahoots and arranged the killings, with both of them doing some killings, and one or the other doing other killings. What I decided about the picture was that all the young men, and the two young women, had all collectively killed Susan's father, which is why they are standing in front of the tank where his body was later discovered (that was the dad's body in the tank at the end, right?). The women had used the men to assist in the killing and carving, and then decided they had to kill the men. Then I'm thinking that Sarah knows she will be killed in Tower Records; she is sacrificing herself so that Susan can go free. This is why the weird look from Susan earlier in the film, when Sarah makes a reference to suicide. Although Sarah is surprised that Susan is the one who actually kills her.

I know Susan was involved in at least one of the killings, because that's why she kills the boy at the beginning of the movie. He peeps over the window edge and sees her at the carving table in her father's old work apartment.

I'm still not sure why the body parts were mixed and matched, or why they were left all over the place. Unless it was to make it look like the work of a deranged person, so they wouldn't be linked to the common cause: Susan.