We keep our chickens fully enclosed inside an Avery, I have never seen the cockerels fight before( we only had 2 but now we have 1 but will be getting rid of him as he attacks me every time I go to the chickens) I find it very unlikely that the other cockerel killed him, he didn’t have any wounds on him so I’m thinking a respiratory problem. Tonight the Alive cockerels comb was bleeding at the back and so was a hen, no predictor would be able to get in at all.
struggling to breath and making squeaking noises when breathing, he had an extremely dark purple comb
Photos of your aviary?
You have a cockerel that is left alive and has a bleeding comb. You have a hen that is/was bleeding at some point too, but don't feel that the cockerel that died could have been in a fight?
If they get kicked in the throat and/or head that sure can cause respiratory distress. Dark purple comb is lack of oxygen.
Blood spattered everywhere...
If you feel it's respiratory disease then refrigerate the body and make arrangements with your vet or agricultural ministry and have testing and necropsy performed.