Badgers are messy killers I've watch them with thermal/nv going along stone walls where new born lambs shelter grabbing hold of and ragging like hell until the lamb dies, guts etc dragged all over the place. fox generally kill quickly and cleanly.
If the head and/or tail are missing 99% of the time it's fox doing the damage, fox with young to feed the carcass usually dissapears without trace (taken back to the earth). I've watch badgers drag the carcass a few hundred yard and have its fill and carry bits away etc but the lamb rarely dissapears without trace if it's a badger
Best to get to the lambing paddocks early and quietly sit and watch, could be a fox doing the killing (geld vixen taking heads and tails) and a badger getting a free meal. Get a good look at the carcass if you can.
Ive seen badgers make a real mess of heavily pregnant ewes that have cest, eating the arse end/udder off them whilst still alive!
They sure as hell don't just eat worms.....