Confused.........the rooster looks like he just dropped dead, except his feathers are everywhere? That sounds like he put up a good fight......didn't just drop dead.
There are patterns to predator behaviors. Yours is a multiple kill, which normally means either raccoons, weasels (or one of the many weasel cousins) or dogs. Raccoons normally eat the heads or some part of them, and it sounds like no dog could get in. That leaves weasels or one of the weasel cousins as the likely culprit.
Weasels are aggressive killers that normally go for the back of the head and neck. There may be missing heads or bite marks on the back of the head and neck......and sometimes not large bite marks.
If so, primary defense is to do the tighten up. No openings anywhere larger than 1/2". That is not easy, but consider this. Likely as not they had a lot of fun last time, so they will be back. Unless you can keep them out, it will keep happening until all you have are gone.