The killers motive.

I'm wondering myself. Just saw it and the whole series this month. For the sake your argument, the flashbacks the killer recalls are weird and present the uncle as a possible weirdo to say the least. The girl heard the killer delusionally ranting about his uncle, and what the girls supposedly did to him, and afterwards sees the photo. She looks between the lines and realizes the uncle may have been too close to the killer as a child. That is possibly why she dramatically lets go of the photo.

Here is what I was wondering. One of the girls, or her family, is somehow connected with the uncle. The girl acts dramatically at the photo (featuring the uncle and killer), but never states what the connection is. They don't even provide a brief flashback to make sense of it. Nobody wants a big speech from the heroine or monologue from the killer anymore nowadays, but they can't just hint at a photo and connection with the heroine/her family, and not say/show what it is. The filmmakers really messed up here...unless there's subtext within the set-up regarding the girl's parents being away, or which parent was away. I wondered if I should have paid more attention to the dialogue concerning one or both parents being away, and if the girl's father is recently deceased...and is the retired cop/uncle who committed suicide. The references to the girl's father fishing and keeping that one fish, stuffed, on display in the basment. But then, the girl already should have known this cousin/killer, and so on. Argh! This is hardly the best slasher film ever made, it is watchable, but the filmmakers missed out on one detail to make it feel whole.

The fact that we do see brief flashbacks, from the killer's point of view, points more to your theory, darth. If the uncle messed with the killer as a child, and the killer randomly/delusionally targeted the group at the beach, they made too big of a deal of the girl seeing the photo at the end. One clue is when the killer is getting hot and heavy with two different girls. When the girls start reaching for his pants and thighs, he suddenly acts sensitively, as if triggered by his uncle's abuse.

I think his cop uncle was pedo and molested him during his childhood (on two occasions he got upset when a girl tried to undo his pants). His uncle then committed suicide due to shame or guilt maybe, and it made the killer trip.

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