Okay so the explanation for "Under the Silver Lake" was so obvious (I thought) that I was waiting for the reveal, and then it never came, and then I looked up explanations online, and they also didn't arrive at the same explanation. So with significant spoilers in mind, here is my theory:
::: Spoilers
Sam is clearly the killer and an unreliable (insane) narrator. Everything in the movie is actually coherent and sensible (well... maybe except for the hobo king), except for scenes that are connected with some severe violence happening to someone who he's alone with, or scenes where he's by himself (figuring out some "hidden code" and deciding that it's leading him to some kind of breakthrough, or wandering around town aimlessly with weird shit happening to him). In no particular order:
- He breaks into the rich guy's house, and it just happens that the guy fits perfectly in with Sam's conspiracy nonsense and also Sam has to kill him
- Right after he gets the gun, when he goes skinny-dipping in the reservoir, the girl he's with mysteriously gets shot
- He hangs out with Sarah, and then she disappears and her roommates all move out immediately and one of them attacks him and runs away when she sees him
- He learns where the conspiracy guy lives, and then right after, the guy gets murdered and when he watches the video, what we're shown happening on the video is weird and semi-supernatural i.e. clearly not what happened in reality
- He beats the shit out of those kids because they keyed his car, but later on, his car is clearly fine, i.e. not keyed after all
- He walks up on the cult people and they talk conspiracy nonsense that fits perfectly with his delusions, and anyway long story short when he walks out they're all dead
Then on top of that, he's carrying dog treats around and in the middle of messing with Sarah's dog when he first meets her. The way the conspiracy reveals itself clearly isn't how it actually happened (it just so happens that the answer is in a Nintendo Power issue he just happens to have with him), this mind-blowingly secret bomb shelter clearly doesn't actually connect to a publicly accessible trapdoor in the back room in the grocery store or whatever, people don't actually start barking at him when they get mad at him. And so on. The guy is just out of his mind and we're seeing a mixture of what really happened and his delusions.
Oh and also he clearly gets excited from thinking about the death of the billionaire; the news story about the billionaire dying is one of the things he lays out for himself to whack off to.
The guy is a serial killer and about half the movie is just wacko stuff that's going on in his mind, and half is real. No? Am I the weird one here?
:::
It's been a few years since I watched it and none of this made sense to me. Just read the Wikipedia summary for a refresher and it's one of the most incomprehensible summaries I've ever read. All I can say is that I remember taking the movie at its word more or less. Interesting idea though.