Taylor, that might not be the best idea. Every betta is different, and it's rather difficult to tell how compatible bettas are with their tank mates until they're actually in there with them.
Is there a possiblity the fish were sick and died and *then* Howl ate them? Did you notice any agression on his part towards them at all, or did he ignore them?
Since you have a practically empty tank, you could consider dividing it with another betta, or maybe planting it heavily and getting a few shrimps and snails and seeing how that goes.