That one hamster of yours is a cannibal. It probably got very, very territorial. This has happened before with other animal species. If they were both stranger males, then yes, this is likely to happen if you do put 2 male animals in a cage. The reason why the one hamster actually ATE their own kind is beyond me.
My fish and my sister's son fish we suggest that we put them together so we can have more fishes /: but they fight with each other till I feel that my fish is going to kill his fish so my sis put her hand and hold the other fish and put it in glass of water it was disgusting moment
The reason for would be if they were same sex or different breed I know because I had an American robo dwarf hamster and a Russian robo dwarf hamster in the same cage they got along fine for a week then the female which was Russian dwarf killed the other so eather yours were same sex although I don't think it should matter because at the pet store they usually have them together the other reason could just be that they were different breed well that's my best answer
NEVER have hamsters live together. They will become very territorial and kill each other after 8 weeks. It was inevitable at any rate. I'm sorry for the loss of your hamster though. Don't be mad at the other hamster though. It was acting upon it's natural instinct.