Vader also wasn't trying to find out if Leia was his daughter at the beginning of A New Hope.
Quote (Flicker69 @ 2 Jan 2016 21:37)
At the end of Star Wars 6, Vader finds out Luke has a sister. And at the end, Vader tells Luke to tell his sister that he was right. That there was good in Vader.
My question is: Does Vader ever find out that his daughter, or Luke's sister, is Leia? The same person Vader captured in the beginning on Episode 4.
No. Vader never finds out Leia is his daughter. Why he couldn't sense her for power I don't know. Why Darth Sidious couldn't sense her power either, I REALLY don't know. It wasn't a concept in Lucas' mind back in 70s probably.