Hi Deb,
It looks like what you have found are the remains of a rabbit.
It would be difficult to say exactly what had killed it but it could easily have been a buzzard.
In my experience, large birds of prey remove the guts first to get at the tasty bits inside such as the heart, liver and kidneys.
Once they have had their fill of all the tasty bits they have no need of the offal and this is usually left to be cleared up by the crows and magpies.
From your photo's the remains look quite fresh. The fact that you did not find a carcass suggests that whatever was feeding on the rabbit was disturbed and either carried or flew off with its meal.
Harrier removing intestines.