Small but rabid dog?
In Adventurer, Conqueror, King System (B/X with some neat extras), as monsters with the ability to 'cleave' (make a second attack after a kill), those critters would eat through 0 Level Henchmen like they were Pringles!
A hermit's catamount?
The PCs. By definition the henchmen's deaths must be the PC's fault. And of course every future hireling will have heard of their cack handed handling of the situation.
Actually, using the 'Mortal Wounds' table from ACKS there was no chance at all to save Merron, one of the Curate's favourite students. But the PCs did have a chance to save Youllon the Crossbowman, but they would have to use the Potion of Healing that Merron had filched from the Chapel. And they would have to do it quick. The party let Youllon bleed out. Calamity! Hammy, their final henchman, a young podgy man-at-arms always moaning about his ill-fitting boots, had to make a morale check. How would he react to the fact that his employers had revealed themselves as callous and calculating. It turned out that the thrill of killing two Lizardman (he applied the finishing blow to two of the four Lizardman that they fought that night) was enough to keep him adventuring. Which isn't to say that this won't come back to bite the PCs in the future...
Oh, and so the answer was, as the players put it, 'Crocoguys'. Luckily I accidentally played them a bit soft, but the players really do need to understand that fighting, in itself, doesn't bring much XP unless it also brings gold. And when what is coming towards you is described as 'a hulking, lizard-headed humanoid, possibly seven foot tall if its mighty thewed shoulders and neck allowed it to stand straight...' it is probably more than a match for a 1st level PC one-on-one. Run away! It's just not worth it!