He was sorry for what he did/what he had done

[emsr2d2]

In some YouTube video the creator of "Game of Thrones" was reading a script and telling actors what the last scene of show is and what they would have to do, and they say " Actor stabs the actress, and she falls, and He looks down and see what he's done.
If we convert it into past, what would we say and what would be the difference?
"He looked down and saw what he did.
"He looked down and saw what he'd done.

All of that information should have been in post #1.