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.