Sounds like a weasel or mink. There might have already been a small tear in the HWC and it may have been weakened with age and the predator just pushed it open enough to get through. Sorry you're dealing with it.
If you wish to dispatch the mink alive use a live trap. Find asuitable spot, dig ahole, secure the cage and camouflage it, ste the trap and pplace the bait, check in the morning