Missing Axolotls

Hi. I have been rearing some axolotls from eggs. I've never done this before, but I've really enjoyed watching them grow and change. They've also attracted a LOT of attention from friends, from friends of friends, from my housemates and their friends, etc. ..
Today i came home to find two had vanished; one of my leucistics (they're about 4 months old and approx 4 - 5 inches in length) and one of my golden albinos (separate tank.. ..about 2 months old, and only just starting to grow rear legs. about 1 - 2 inches each). whilst i could believe that the golden albinos had maybe eaten their sibling, i just find it difficult to believe that the leucistics could have...they're pretty big and the water wasn't different from normal.
I am basically trying to gain some opinions on whether it is possible or likely the leucistics ate their mate (leaving NO signs. ..no bloody water or body parts our anything)? i doubt want to think that my housemates may have pinched some for mates who have shown interest.. .any thoughts, or alternative suggestions?

Is there a lid to the tank and how far from the top of the tank is the water level? You could have a jumper. However, the fact that two axolotls, from two different tanks are gone at the same time, I would ask your roommates.
If the siblings did turn cannibalistic, you would find SOME remains.