Raccoons based on following.
Raccoons - feathers have slobbery look, bones chewed through, multiple victims on a single visit, work sometimes as family group
Possums - often chews through to dismember but does not work as a group so likely only one bird attacked and only it dismembered. Feathers can have slobbery look
Coyotes - move prey off rarely eating on site
Hawks - de-feathering extensive with plucked feathers appearing dry. Does not dismember by chewing through, rather by tearing.
If birds left, then either tighten up that pen big time or move them. Consider setting up a live trap or two. When I do not have proper defenses in place I sleep with window open and have weapon and flashlite at ready by door. During day tighten up that coop.