What do I do??

[Wyorp Rock]

They've done excellent with previous cockerels so I'm not sure what set them off with this one since they finally accepted him weeks ago.
Another reason I'm heartbroken, is he never crowed so we didn't have any issues with our neighbors

Oh, I thought maybe he crowed a lot since it looks like he had a no crow collar on.

Not all roosters make good flock masters.
I've had hens "tolerate" a rooster/cockerels presence but they never "warmed up" to him. Not

 

[KikiDeAnime]

Oh, I thought maybe he crowed a lot since it looks like he had a no crow collar on.

Not all roosters make good flock masters.
I've had hens "tolerate" a rooster/cockerels presence but they never "warmed up" to him. Not

He did wear one. It was just in case he attempted to crow. I had to be prepared. He wore it loosely.

 

[Chickassan]

Things happen with chickens sometimes that even people who have kept them for years don't understand what exactly happened.
I have personally had a flock come close to killing a perfectly healthy looking and acting male in a situation where space wasn't an issue neither was familiarity.
No idea what sparked it.
They never did it to another one.
Culling isn't an answer to a question you don't understand.
My condolences on your fella, and please don't be hard on yourself.

.

 

[aart]

I have never in all my years of chicken keeping had hens attack and kill another chicken

I've seen birds go after a bird that died suddenly.
Heard a scuffle(not unusual),
then a flapflapflap(sounded like a death throe flapping-which got me running out to see),
cock and a hen were exuberantly pecking at a downed hen.
Think the hen panicked and flew into fencing, breaking her neck,
the death throes stimulated the other 2 to peck at the dead one.