I had a sparrow hawk pulling growers through the bars of a cage. Actually caught it in the act so no doubt. I put extra, finer size wire around the base of the pen and no more deaths, but I did see it back on the lawn, hopping about the cage.
Also had a cat who learned to pull half grown chicks through the 'hand holder holes' of a pen years ago.
And my neighbour, years ago told me about a mistery; she would find them picked clean inside their pen, only with no skull/head! Eventually saw a fox sitting beside them and realised it must have waited for them to poke their heads out to get the long strands of grass, bit it off and the remaining hens in the pen must have done the rest!