Peppermint Shrimp?

[Kait]

I have a peppermint in my tank that zooms around, he's always out and is just a delight to watch. The two in my boyfriend' stank do not come out for food. We can see them chilling in the little spots, and you can rarely see them zooming around the tank at night, but they don't come out for food.

I doubt the one killed the other, however, they are opportunistic eaters, and would likely munch on the carcass of one that died. It's possible that the second one just didn't make it over night.