Sad and angry. What did this? (Photos, not too gruesome)

[JacinLarkwell]

I would say either a feral cat or a coyote. Out coyotes always carry a bird off, leaving just feathers, but we had a feral cat that killed a hen and then ate it right in my horse stall with my mare

 

[TARDIS37379]

Sounds like your neighbors are just a bit lax at caring for chickens.

 

[MysteryChicken]

Cats like to gut their prey, so I believe it's a cat.
I can't find pictures of this for comparison surprisingly.
Cats usually eat the entire prey animal, depending on size, if it's a larger animal like an adult hen, they'd leave the wings, legs, & occasionally the head of the chicken.

 

[NatJ]

That looks a lot like the work of a dog or coyote to me.

Most pet dogs will not actually eat a bird that they kill, and they tend to run around chasing and killing more birds just for the fun. (Basically, they play instead of hunting for food.)

I am sure this was an animal hunting for food. If it was a dog, it was an unusual dog. A stray that has been hunting its own food for a while might have learned to kill efficiently and eat while leaving the other birds for later.