Why would a superbly-trained, 5 year-old, purebred German Shepard suddenly attack his handler?

A lot of factors can cause something like that. Even a well trained animal can become frighted, aggressive, or both. Sometimes the triggers are medical while other times it is environmental. Likely he wasn't provoked or any such thing. There are known cases where a sudden environmental change has caused an animal not to recognize its owner/trainer- a shift in stance/emotion of the person or a some unrecognizable odor. There are also cases where the environment change is not connected directly to the owner/trainer but unfortunately they are the closest object to let out the aggression/fear on. Medical triggers are similar to environmental ones but instead of the environment itself changing the animal's perspective of that environment is what has changed. All it really takes is a split second of nonrecognition, sometimes there is nothing that can be done to stop the animal once they are afraid and/or aggressive.

Medical issue.

This is the only reason I can think of, the dog might have had a brain tumor or some other medical issue that caused it to 'snap'.

Or as another mentioned, it could has weak nerves.

**Shows how much I pay attention- Didn't even notice Shepherd was spelled wrong*** Domino makes good points.

No dog attacks without a reason, so either the dog didn't trust the handler that well, or he did something wrong.

And it is Shepherd, not shephard.

The dog was punished one too many times.

i think there more to this story,i had a german shepard,she was the best! they wouldn t attack you,sound like you did something!

as vague as your question sounds, i think that the shepherd may have done something to aggravate him, or maybe it could be medical

why does a seemingly normal person become a murderer? Sometimes things dont make sense

nervous dog

Because the trainer smelled like ****.