Even if you have possums in the area and catch one in a trap, I would suspect that the culprit might have been a rat. They can get into pretty small holes and have been known to eat limbs off live chicks.
We've caught FIVE possums here in the last four days, and another was killed in the road. The one last night was 1 foot away from a duck setting on eggs. I hate to think of what would have happened had he gone one foot the other way to her.
That's a total of six possums - that we KNOW of and took care of - within four weeks.