Fox cub killed ! (1 Viewer)

A friend at work has had 3 fox cubs coming into his garden nightly for the last couple of months sometimes with the parents but more than often on their own. Last saturday he fed them as usual and filmed them around 11 oclock then at around 4 oclock was awoken by in his words " something screaming in the garden" looking out he saw an adult fox with one of the cubs in it's mouth and shaking it by the neck quickly throwing some clothes on he rushed outside but it was unfortunatly to late for the cub who died from a large wound in it's neck shortly after.
Has anyone heard of this happening before and/or got any explaination as to why this occured ?
The cub was female so that would rule out male rivallry and the other 2 cubs are still around yet now very timid
Could this have been a rogue dog passing thro or is it likely to return and attack the other 2 ?
Any ideas? please

I have heard of cases in the animal world where a male will kill young to bring the mother into heat again but I don't know if this applies to foxes too or not. A crying shame about the pup tho'.

What a shame Simon