Is this a common occurrence in your ASF colony or a one time thing? Are you sure this animal was alive 20 minutes earlier or could it have already expired in a corner and was simply being eaten as most rodents will utilize a free source of protein? More information might help to understand why this has occurred.
I house about 7 males together and I have 7 trios in a mouse rack and I've never seen anything like that. I only had one male killed in the first 2 weeks that i got the colony and a couple babies that might have died because the mother did keep some from that litter so my guess is they were sick or stillborn.. I would make sure the water bottles aren't getting clogged and feed them a little more so they never run out if you don't already. If it was a male with other males, then there's your problem and it'll probably happen again until you find the "zombie." If you're sure it happened very recently, next time check their noses for blood, hard to go "zombie" without some blood on your face...feed him off and move on...
i got a few questions how many per tub and sex ratio size of tub what kinda feed and protein content. also is it related to the others in the tub or not. on a side note so far this is pretty random from what ive found but im trying to find actual factors that lead to this