Who killed the dogs?

One of the many plot holes in the movie.

All the signs and analysis I watched say it's Sam. I find that the least interesting part of the movie though and definitely makes him unlikeable

I know this is an old post but I just saw the movie this week and was looking up discussions of it ...

I'm wondering if the dogs were sacrificed to power the secret cabal's "transition" to their higher consciousness; blood sacrifices. They seem to be happening around the same time. Similarly, I think the oddly timed fireworks show signals a group's transition. You can tell it disturbs Sarah--because she knows what it means--while it just kind of confuses Sam.

Andrew Garfield's character Sam is the dogkiller. Here are some clues:

1. Sam first notices Riley Keough's character because he sees her dog. It appears he uses the dog to get closer to her, but maybe he uses her to get closer to her dog.

2. Sam has a nightmare where he sees himself mutilating and eating a dog.

3. Sam is frequented by dreams, visions, and hallucinations of women barking at him like dogs.

4. While walking with the billionaire's daughter at night, Sam is asked if he's a dog person or a cat person. Sam tells a story about how his grandpa's dog attacked him as a kid, so he's likely more of a cat person. This hints at a lifelong animosity towards dogs.

5. In the same conversation as #4, Sam says he's not afraid of walking around at night because the dogkiller only kills dogs. She asks "it wouldn't take much for dog killer to try and kill a human, right?" and he confidently says "no." Why is he so sure? This implies he knows exactly how the dogkiller thinks, but how would he if it's not him or someone he knows?

6. Sam follows coyotes around. This can be interpreted as Sam trying to kill an exotic or next-level dog, or because Sam could be tracking it, since coyotes kill more domesticated dogs than any other animal in America. Maybe Sam sees himself as a coyote, stalking and killing dogs like a coyote would.

7. While reading about the dogkiller in his apartment, Sam watches Invasion Of The Body Snatchers, a film with an unreliable protagonist who may be killing people.

8. Sam really wants to meet the comic book artist who made artwork about the dogkiller, for no reason other than it'd be cool to meet him, I guess. Seems to me Sam was flattered by the comic and wants to meet a fan.

9. At the end of the film, Sam is questioned why he's carrying dog treats in his pockets. He claims it's because he was trying to win over a girl who had a dog, but the dog treats in his pockets are the same ones that the dogkiller uses to lure dogs, and are the same treats seen in all of Sam's dreams. This one feels very definitive to me.

10. Sam clearly has very violent tendencies and overreacts to several situations by brutally assaulting or even murdering his foes.