Male dogs behavior

Question
What would cause a male Yorkie to attack and kill an 8 week old puppy? The male is the father of the liter and has been exposed to the liter the entire time.

Answer
This is a very difficult question because I can't put hands on the dog and don't have the opportunity to question you at length regarding past behavior toward other dogs and yourselves.  I suggest you immediately remove this dog from the remaining pups and, due to this incident, I would strongly advise you to neuter him and not to breed him again.