why he <had><has> left

[jun12]

I was watching a movie with my friend.

In the movie, A had left his hometown because of something but he came back with some kind of purpose. While B found the (thing) that made A to leave his hometown.

In that scene my friend asked me "What is that?"

In this case which answer should I use in these three sentences?

1 : "That is the reason why he had left his hometown."
2 : "That is the reason why he has left his hometown."
3 : "That is the reason why he left his hometown."

I think 1 is right but I heard somewhere that I should put past tense phrase to make had P.P work.
So I'm a little bit confused because of this.

Thank you.

 

[PaulQ]

"What is that?"

- this only works if the "thing" is a real object, not abstract, i.e. it cannot be a concept, idea, emotion, set of circumstances, etc

1 : "That is the reason why he had left his hometown."
2 : "That is the reason why he has left his hometown."
3 : "That is the reason why he left his hometown."

That is why he left.

 

[se16teddy]

1 : "That is the reason why he had left his hometown."
2 : "That is the reason why he has left his hometown."
3 : "That is the reason why he left his hometown."

Does the speaker wish to emphasize or clarify that “leaving” happened before something else that the speaker has in mind? (1)
Does the speaker mean that this is the reason why he is not in his hometown now? (2)
If neither, probably (3) is best.